bad performance on RAID 5

bad performance on RAID 5

[Sevrin Robstad]

I'm suffering from bad performance on my RAID5.

a "echo check >/sys/block/md0/md/sync_action"

gives a speed at only about 5000K/sec , and HIGH load average :

# uptime
20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52

kernel is 2.6.18.1.2257.fc5
mdadm is v2.5.5

the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA PCI 
cards with a total of 6  250gb S-ATA drives connected.

[root@compaq ~]# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.03
  Creation Time : Tue Dec  5 00:33:01 2006
     Raid Level : raid5
     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
    Device Size : 243786240 (232.49 GiB 249.64 GB)
   Raid Devices : 6
  Total Devices : 6
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Wed Jan 17 23:14:39 2007
          State : clean
 Active Devices : 6
Working Devices : 6
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 256K

           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
         Events : 0.58

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       3       8       49        3      active sync   /dev/sdd1
       4       8       65        4      active sync   /dev/sde1
       5       8       81        5      active sync   /dev/sdf1
[root@compaq ~]#


Sevrin

Re: bad performance on RAID 5

[Justin Piszcz]

Sevrin Robstad wrote:
> I'm suffering from bad performance on my RAID5.
>
> a "echo check >/sys/block/md0/md/sync_action"
>
> gives a speed at only about 5000K/sec , and HIGH load average :
>
> # uptime
> 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
>
> kernel is 2.6.18.1.2257.fc5
> mdadm is v2.5.5
>
> the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA 
> PCI cards with a total of 6  250gb S-ATA drives connected.
>
> [root@compaq ~]# mdadm --detail /dev/md0
> /dev/md0:
>        Version : 00.90.03
>  Creation Time : Tue Dec  5 00:33:01 2006
>     Raid Level : raid5
>     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
>    Device Size : 243786240 (232.49 GiB 249.64 GB)
>   Raid Devices : 6
>  Total Devices : 6
> Preferred Minor : 0
>    Persistence : Superblock is persistent
>
>    Update Time : Wed Jan 17 23:14:39 2007
>          State : clean
> Active Devices : 6
> Working Devices : 6
> Failed Devices : 0
>  Spare Devices : 0
>
>         Layout : left-symmetric
>     Chunk Size : 256K
>
>           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
>         Events : 0.58
>
>    Number   Major   Minor   RaidDevice State
>       0       8        1        0      active sync   /dev/sda1
>       1       8       17        1      active sync   /dev/sdb1
>       2       8       33        2      active sync   /dev/sdc1
>       3       8       49        3      active sync   /dev/sdd1
>       4       8       65        4      active sync   /dev/sde1
>       5       8       81        5      active sync   /dev/sdf1
> [root@compaq ~]#
>
>
> Sevrin
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

If they are on the PCI bus, that is about right, you probably should be 
getting 10-15MB/s, but it is about right.  If you had each drive on its 
own PCI-e controller, then you would get much faster speeds.

Re: bad performance on RAID 5

[Raz Ben-Jehuda(caro)]

did u  increase the stripe cache size ?


On 1/18/07, Justin Piszcz <jpiszcz@lucidpixels.com> wrote:
> Sevrin Robstad wrote:
> > I'm suffering from bad performance on my RAID5.
> >
> > a "echo check >/sys/block/md0/md/sync_action"
> >
> > gives a speed at only about 5000K/sec , and HIGH load average :
> >
> > # uptime
> > 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
> >
> > kernel is 2.6.18.1.2257.fc5
> > mdadm is v2.5.5
> >
> > the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA
> > PCI cards with a total of 6  250gb S-ATA drives connected.
> >
> > [root@compaq ~]# mdadm --detail /dev/md0
> > /dev/md0:
> >        Version : 00.90.03
> >  Creation Time : Tue Dec  5 00:33:01 2006
> >     Raid Level : raid5
> >     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
> >    Device Size : 243786240 (232.49 GiB 249.64 GB)
> >   Raid Devices : 6
> >  Total Devices : 6
> > Preferred Minor : 0
> >    Persistence : Superblock is persistent
> >
> >    Update Time : Wed Jan 17 23:14:39 2007
> >          State : clean
> > Active Devices : 6
> > Working Devices : 6
> > Failed Devices : 0
> >  Spare Devices : 0
> >
> >         Layout : left-symmetric
> >     Chunk Size : 256K
> >
> >           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
> >         Events : 0.58
> >
> >    Number   Major   Minor   RaidDevice State
> >       0       8        1        0      active sync   /dev/sda1
> >       1       8       17        1      active sync   /dev/sdb1
> >       2       8       33        2      active sync   /dev/sdc1
> >       3       8       49        3      active sync   /dev/sdd1
> >       4       8       65        4      active sync   /dev/sde1
> >       5       8       81        5      active sync   /dev/sdf1
> > [root@compaq ~]#
> >
> >
> > Sevrin
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
> If they are on the PCI bus, that is about right, you probably should be
> getting 10-15MB/s, but it is about right.  If you had each drive on its
> own PCI-e controller, then you would get much faster speeds.
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>


-- 
Raz

Re: bad performance on RAID 5

[Sevrin Robstad]

Justin Piszcz wrote:
>> I'm suffering from bad performance on my RAID5.
>>
>> a "echo check >/sys/block/md0/md/sync_action"
>>
>> gives a speed at only about 5000K/sec , and HIGH load average :
>>
>> # uptime
>> 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
>>
>> kernel is 2.6.18.1.2257.fc5
>> mdadm is v2.5.5
>>
>> the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA 
>> PCI cards with a total of 6  250gb S-ATA drives connected.
>>
>> [root@compaq ~]# mdadm --detail /dev/md0
>> /dev/md0:
>>        Version : 00.90.03
>>  Creation Time : Tue Dec  5 00:33:01 2006
>>     Raid Level : raid5
>>     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
>>    Device Size : 243786240 (232.49 GiB 249.64 GB)
>>   Raid Devices : 6
>>  Total Devices : 6
>> Preferred Minor : 0
>>    Persistence : Superblock is persistent
>>
>>    Update Time : Wed Jan 17 23:14:39 2007
>>          State : clean
>> Active Devices : 6
>> Working Devices : 6
>> Failed Devices : 0
>>  Spare Devices : 0
>>
>>         Layout : left-symmetric
>>     Chunk Size : 256K
>>
>>           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
>>         Events : 0.58
>>
>>    Number   Major   Minor   RaidDevice State
>>       0       8        1        0      active sync   /dev/sda1
>>       1       8       17        1      active sync   /dev/sdb1
>>       2       8       33        2      active sync   /dev/sdc1
>>       3       8       49        3      active sync   /dev/sdd1
>>       4       8       65        4      active sync   /dev/sde1
>>       5       8       81        5      active sync   /dev/sdf1
>> [root@compaq ~]#
>>
>>
>> Sevrin
>> -
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
> If they are on the PCI bus, that is about right, you probably should 
> be getting 10-15MB/s, but it is about right.  If you had each drive on 
> its own PCI-e controller, then you would get much faster speeds.
>
>

There are two controllers, 4 disks connected to one controller on the 
PCI-bus and 2 disks connected to the other controller.
As you say I should have had 10-15MB/s, but I'm having 5MB *and* with 
really high load average.

Sevrin

Re: bad performance on RAID 5

[Sevrin Robstad]

I've tried to increase the cache size - I can't measure any difference.....

Raz Ben-Jehuda(caro) wrote:
> did u  increase the stripe cache size ?
>
>
> On 1/18/07, Justin Piszcz <jpiszcz@lucidpixels.com> wrote:
>> Sevrin Robstad wrote:
>> > I'm suffering from bad performance on my RAID5.
>> >
>> > a "echo check >/sys/block/md0/md/sync_action"
>> >
>> > gives a speed at only about 5000K/sec , and HIGH load average :
>> >
>> > # uptime
>> > 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
>> >
>> > kernel is 2.6.18.1.2257.fc5
>> > mdadm is v2.5.5
>> >
>> > the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA
>> > PCI cards with a total of 6  250gb S-ATA drives connected.
>> >
>> > [root@compaq ~]# mdadm --detail /dev/md0
>> > /dev/md0:
>> >        Version : 00.90.03
>> >  Creation Time : Tue Dec  5 00:33:01 2006
>> >     Raid Level : raid5
>> >     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
>> >    Device Size : 243786240 (232.49 GiB 249.64 GB)
>> >   Raid Devices : 6
>> >  Total Devices : 6
>> > Preferred Minor : 0
>> >    Persistence : Superblock is persistent
>> >
>> >    Update Time : Wed Jan 17 23:14:39 2007
>> >          State : clean
>> > Active Devices : 6
>> > Working Devices : 6
>> > Failed Devices : 0
>> >  Spare Devices : 0
>> >
>> >         Layout : left-symmetric
>> >     Chunk Size : 256K
>> >
>> >           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
>> >         Events : 0.58
>> >
>> >    Number   Major   Minor   RaidDevice State
>> >       0       8        1        0      active sync   /dev/sda1
>> >       1       8       17        1      active sync   /dev/sdb1
>> >       2       8       33        2      active sync   /dev/sdc1
>> >       3       8       49        3      active sync   /dev/sdd1
>> >       4       8       65        4      active sync   /dev/sde1
>> >       5       8       81        5      active sync   /dev/sdf1
>> > [root@compaq ~]#
>> >
>> >
>> > Sevrin
>> > -
>> > To unsubscribe from this list: send the line "unsubscribe 
>> linux-raid" in
>> > the body of a message to majordomo@vger.kernel.org
>> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>> If they are on the PCI bus, that is about right, you probably should be
>> getting 10-15MB/s, but it is about right.  If you had each drive on its
>> own PCI-e controller, then you would get much faster speeds.
>>
>> -
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
>

Re: bad performance on RAID 5

[Steve Cousins]

Sevrin Robstad wrote:
> I'm suffering from bad performance on my RAID5.
> 
> a "echo check >/sys/block/md0/md/sync_action"
> 
> gives a speed at only about 5000K/sec , and HIGH load average :

What do you get when you try something like:

time dd if=/dev/zero of=/mount-point/test.dat bs=1024k count=1024

where /mount-point is where /dev/md0 is mounted.

This will create a 1 GiB file and it will tell you how long it takes to 
create it.  Also, I'd try running Bonnie++ on it to see what the 
different performance values are.

I don't know a lot about the md sync process but I remember having my 
sync action stuck at a low value at one point and it didn't have 
anything to do with the performance of the RAID array in general.

Steve

> # uptime
> 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
> 
> kernel is 2.6.18.1.2257.fc5
> mdadm is v2.5.5
> 
> the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA PCI 
> cards with a total of 6  250gb S-ATA drives connected.
> 
> [root@compaq ~]# mdadm --detail /dev/md0
> /dev/md0:
>        Version : 00.90.03
>  Creation Time : Tue Dec  5 00:33:01 2006
>     Raid Level : raid5
>     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
>    Device Size : 243786240 (232.49 GiB 249.64 GB)
>   Raid Devices : 6
>  Total Devices : 6
> Preferred Minor : 0
>    Persistence : Superblock is persistent
> 
>    Update Time : Wed Jan 17 23:14:39 2007
>          State : clean
> Active Devices : 6
> Working Devices : 6
> Failed Devices : 0
>  Spare Devices : 0
> 
>         Layout : left-symmetric
>     Chunk Size : 256K
> 
>           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
>         Events : 0.58
> 
>    Number   Major   Minor   RaidDevice State
>       0       8        1        0      active sync   /dev/sda1
>       1       8       17        1      active sync   /dev/sdb1
>       2       8       33        2      active sync   /dev/sdc1
>       3       8       49        3      active sync   /dev/sdd1
>       4       8       65        4      active sync   /dev/sde1
>       5       8       81        5      active sync   /dev/sdf1
> [root@compaq ~]#
> 
> 
> Sevrin
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
______________________________________________________________________
  Steve Cousins, Ocean Modeling Group    Email: cousins@umit.maine.edu
  Marine Sciences, 452 Aubert Hall       http://rocky.umeoce.maine.edu
  Univ. of Maine, Orono, ME 04469        Phone: (207) 581-4302

Re: bad performance on RAID 5

[Mark Hahn]

>>> gives a speed at only about 5000K/sec , and HIGH load average :
>>> # uptime
>>> 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52

loadav is a bit misleading - it doesn't mean you had >11 runnable jobs.
you might just have more jobs waiting on IO, being starved by the 
IO done by resync.

>>>     Chunk Size : 256K

well, that's pretty big.  it means 6*256K is necessary to do a 
whole-stripe update; your stripe cache may be too small to be effective.

>> If they are on the PCI bus, that is about right, you probably should be 
>> getting 10-15MB/s, but it is about right.  If you had each drive on its own 
>> PCI-e controller, then you would get much faster speeds.

10-15 seems bizarrely low - one can certainly achieve >100 MB/s
over the PCI bus, so where does the factor of 6-10 come in?
seems like a R6 resync would do 4 reads and 2 writes for every
4 chunks of throughput (so should achieve more like 50 MB/s if 
the main limit is the bus at 100.)

> There are two controllers, 4 disks connected to one controller on the PCI-bus 
> and 2 disks connected to the other controller.

well, you should probably look at the PCI topology ("lspci -v -t"),
and perhaps even the PCI settings (as well as stripe cache size, 
perhaps nr_requests, etc)

Re: bad performance on RAID 5

[Raz Ben-Jehuda(caro)]

iorder to understand what is going in your system you should:
1. determine the access pattern to the volume. meaning:
     sequetial ? random access ?
     sync io ? async io ?
     mostly read ? mostly write ?
     Are you using small buffers ?  big buffers ?

2. you should test the controller capabilty.
     meaning :
     see if dd'in for each disk in the system seperately reduces the total
      throughput.


On 1/18/07, Sevrin Robstad <quackyo@start.no> wrote:
> I've tried to increase the cache size - I can't measure any difference.....
>
> Raz Ben-Jehuda(caro) wrote:
> > did u  increase the stripe cache size ?
> >
> >
> > On 1/18/07, Justin Piszcz <jpiszcz@lucidpixels.com> wrote:
> >> Sevrin Robstad wrote:
> >> > I'm suffering from bad performance on my RAID5.
> >> >
> >> > a "echo check >/sys/block/md0/md/sync_action"
> >> >
> >> > gives a speed at only about 5000K/sec , and HIGH load average :
> >> >
> >> > # uptime
> >> > 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
> >> >
> >> > kernel is 2.6.18.1.2257.fc5
> >> > mdadm is v2.5.5
> >> >
> >> > the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA
> >> > PCI cards with a total of 6  250gb S-ATA drives connected.
> >> >
> >> > [root@compaq ~]# mdadm --detail /dev/md0
> >> > /dev/md0:
> >> >        Version : 00.90.03
> >> >  Creation Time : Tue Dec  5 00:33:01 2006
> >> >     Raid Level : raid5
> >> >     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
> >> >    Device Size : 243786240 (232.49 GiB 249.64 GB)
> >> >   Raid Devices : 6
> >> >  Total Devices : 6
> >> > Preferred Minor : 0
> >> >    Persistence : Superblock is persistent
> >> >
> >> >    Update Time : Wed Jan 17 23:14:39 2007
> >> >          State : clean
> >> > Active Devices : 6
> >> > Working Devices : 6
> >> > Failed Devices : 0
> >> >  Spare Devices : 0
> >> >
> >> >         Layout : left-symmetric
> >> >     Chunk Size : 256K
> >> >
> >> >           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
> >> >         Events : 0.58
> >> >
> >> >    Number   Major   Minor   RaidDevice State
> >> >       0       8        1        0      active sync   /dev/sda1
> >> >       1       8       17        1      active sync   /dev/sdb1
> >> >       2       8       33        2      active sync   /dev/sdc1
> >> >       3       8       49        3      active sync   /dev/sdd1
> >> >       4       8       65        4      active sync   /dev/sde1
> >> >       5       8       81        5      active sync   /dev/sdf1
> >> > [root@compaq ~]#
> >> >
> >> >
> >> > Sevrin
> >> > -
> >> > To unsubscribe from this list: send the line "unsubscribe
> >> linux-raid" in
> >> > the body of a message to majordomo@vger.kernel.org
> >> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>
> >> If they are on the PCI bus, that is about right, you probably should be
> >> getting 10-15MB/s, but it is about right.  If you had each drive on its
> >> own PCI-e controller, then you would get much faster speeds.
> >>
> >> -
> >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> >> the body of a message to majordomo@vger.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>
> >
> >
>
>


-- 
Raz

Re: bad performance on RAID 5

[Sevrin Robstad]

Steve Cousins wrote:
> Sevrin Robstad wrote:
>> I'm suffering from bad performance on my RAID5.
>>
>> a "echo check >/sys/block/md0/md/sync_action"
>>
>> gives a speed at only about 5000K/sec , and HIGH load average :
> What do you get when you try something like:
>
> time dd if=/dev/zero of=/mount-point/test.dat bs=1024k count=1024
>
> where /mount-point is where /dev/md0 is mounted.
>
> This will create a 1 GiB file and it will tell you how long it takes 
> to create it.  Also, I'd try running Bonnie++ on it to see what the 
> different performance values are.
>
> I don't know a lot about the md sync process but I remember having my 
> sync action stuck at a low value at one point and it didn't have 
> anything to do with the performance of the RAID array in general.
>

I ran the a couple of times, and got either about 28MB/s or about 
34MB/s. strange.
When I run the same test on a single disk connected to another 
controller I get about 60MB/s.


[root@compaq ~]# time dd if=/dev/zero of=/mnt/gigaraid/1gb.testfile 
bs=1024k cou   nt=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 38.1873 seconds, 28.1 MB/s

real    0m38.321s
user    0m0.009s
sys     0m8.602s
[root@compaq ~]# time dd if=/dev/zero of=/mnt/gigaraid/1gb.testfile 
bs=1024k cou   nt=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 31.4377 seconds, 34.2 MB/s

real    0m31.949s
user    0m0.016s
sys     0m8.988s
[root@compaq ~]# time dd if=/dev/zero of=/mnt/gigaraid/1gb.testfile 
bs=1024k cou   nt=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 37.599 seconds, 28.6 MB/s

real    0m38.151s
user    0m0.011s
sys     0m9.291s
[root@compaq ~]# time dd if=/dev/zero of=/mnt/gigaraid/1gb.testfile 
bs=1024k count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 31.2569 seconds, 34.4 MB/s

real    0m31.765s
user    0m0.007s
sys     0m8.913s
[root@compaq ~]# time dd if=/dev/zero of=/mnt/gigaraid/1gb.testfile 
bs=1024k count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 37.4778 seconds, 28.7 MB/s

real    0m37.923s
user    0m0.009s
sys     0m9.231s

Re: bad performance on RAID 5

[Sevrin Robstad]

Mark Hahn wrote:
>>>     Chunk Size : 256K
>
> well, that's pretty big.  it means 6*256K is necessary to do a 
> whole-stripe update; your stripe cache may be too small to be effective.
>
>>> If they are on the PCI bus, that is about right, you probably should 
>>> be getting 10-15MB/s, but it is about right.  If you had each drive 
>>> on its own PCI-e controller, then you would get much faster speeds.
>
> 10-15 seems bizarrely low - one can certainly achieve >100 MB/s
> over the PCI bus, so where does the factor of 6-10 come in?
> seems like a R6 resync would do 4 reads and 2 writes for every
> 4 chunks of throughput (so should achieve more like 50 MB/s if the 
> main limit is the bus at 100.)
>
>> There are two controllers, 4 disks connected to one controller on the 
>> PCI-bus and 2 disks connected to the other controller.
>
> well, you should probably look at the PCI topology ("lspci -v -t"),
> and perhaps even the PCI settings (as well as stripe cache size, 
> perhaps nr_requests, etc)
>
>
I've tried to increase the stripe_cache_size a lot, no noticable difference.
I set it to 8096....

[root@compaq md]# lspci -v -t
-[0000:00]-+-00.0  VIA Technologies, Inc. VT8366/A/7 [Apollo KT266/A/333]
           +-01.0-[0000:01]----00.0  ATI Technologies Inc Rage 128 RF/SG AGP
           +-05.0  Silicon Image, Inc. SiI 3114 [SATALink/SATARaid] 
Serial ATA Controller
           +-07.0  Silicon Image, Inc. SiI 3114 [SATALink/SATARaid] 
Serial ATA Controller
           +-08.0  Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit Ethernet
           +-11.0  VIA Technologies, Inc. VT8233 PCI to ISA Bridge
           \-11.1  VIA Technologies, Inc. 
VT82C586A/B/VT82C686/A/B/VT823x/A/C PIPC Bus Master IDE
[root@compaq md]#

Re: bad performance on RAID 5

[Bill Davidsen]

Sevrin Robstad wrote:
> I've tried to increase the cache size - I can't measure any 
> difference.....

You probably won't help small writes, but large writes will go faster 
with a stripe cache of size num_disks*chunk_size*2 or larger.
>
> Raz Ben-Jehuda(caro) wrote:
>> did u  increase the stripe cache size ?
>>
>>
>> On 1/18/07, Justin Piszcz <jpiszcz@lucidpixels.com> wrote:
>>> Sevrin Robstad wrote:
>>> > I'm suffering from bad performance on my RAID5.
>>> >
>>> > a "echo check >/sys/block/md0/md/sync_action"
>>> >
>>> > gives a speed at only about 5000K/sec , and HIGH load average :
>>> >
>>> > # uptime
>>> > 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
>>> >
>>> > kernel is 2.6.18.1.2257.fc5
>>> > mdadm is v2.5.5
>>> >
>>> > the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA
>>> > PCI cards with a total of 6  250gb S-ATA drives connected.
>>> >
>>> > [root@compaq ~]# mdadm --detail /dev/md0
>>> > /dev/md0:
>>> >        Version : 00.90.03
>>> >  Creation Time : Tue Dec  5 00:33:01 2006
>>> >     Raid Level : raid5
>>> >     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
>>> >    Device Size : 243786240 (232.49 GiB 249.64 GB)
>>> >   Raid Devices : 6
>>> >  Total Devices : 6
>>> > Preferred Minor : 0
>>> >    Persistence : Superblock is persistent
>>> >
>>> >    Update Time : Wed Jan 17 23:14:39 2007
>>> >          State : clean
>>> > Active Devices : 6
>>> > Working Devices : 6
>>> > Failed Devices : 0
>>> >  Spare Devices : 0
>>> >
>>> >         Layout : left-symmetric
>>> >     Chunk Size : 256K
>>> >
>>> >           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
>>> >         Events : 0.58
>>> >
>>> >    Number   Major   Minor   RaidDevice State
>>> >       0       8        1        0      active sync   /dev/sda1
>>> >       1       8       17        1      active sync   /dev/sdb1
>>> >       2       8       33        2      active sync   /dev/sdc1
>>> >       3       8       49        3      active sync   /dev/sdd1
>>> >       4       8       65        4      active sync   /dev/sde1
>>> >       5       8       81        5      active sync   /dev/sdf1
>>> > [root@compaq ~]#
>>> >
>>> >
>>> > Sevrin
>>> > -
>>> > To unsubscribe from this list: send the line "unsubscribe 
>>> linux-raid" in
>>> > the body of a message to majordomo@vger.kernel.org
>>> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>> If they are on the PCI bus, that is about right, you probably should be
>>> getting 10-15MB/s, but it is about right.  If you had each drive on its
>>> own PCI-e controller, then you would get much faster speeds. 


-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

Re: bad performance on RAID 5

[Bill Davidsen]

) Steve Cousins wrote:
> Sevrin Robstad wrote:
>> I'm suffering from bad performance on my RAID5.
>>
>> a "echo check >/sys/block/md0/md/sync_action"
>>
>> gives a speed at only about 5000K/sec , and HIGH load average :
>
> What do you get when you try something like:
>
> time dd if=/dev/zero of=/mount-point/test.dat bs=1024k count=1024
That doesn't give valid (repeatable) results due to caching issues. Go 
back to the thread I started on RAID-5 write, and see my results. More 
important, the way I got rid of the cache effects (beside an unloaded 
systems) was:
  sync; time bash -c "dd if=/dev/zero bs=1024k count=2048 
of=/mnt/point/file; sync"
I empty the cache, then time the dd including the sync at the end. 
Results are far more repeatable.

I actually was able to create custom arrays on unused devices to play 
with array setting, once you use the array you can't tune as much.
>
> where /mount-point is where /dev/md0 is mounted.
>
> This will create a 1 GiB file and it will tell you how long it takes 
> to create it.  Also, I'd try running Bonnie++ on it to see what the 
> different performance values are.
>
> I don't know a lot about the md sync process but I remember having my 
> sync action stuck at a low value at one point and it didn't have 
> anything to do with the performance of the RAID array in general.
>
> Steve
>
>> # uptime
>> 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
>>
>> kernel is 2.6.18.1.2257.fc5
>> mdadm is v2.5.5
>>
>> the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA 
>> PCI cards with a total of 6  250gb S-ATA drives connected.
>>
>> [root@compaq ~]# mdadm --detail /dev/md0
>> /dev/md0:
>>        Version : 00.90.03
>>  Creation Time : Tue Dec  5 00:33:01 2006
>>     Raid Level : raid5
>>     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
>>    Device Size : 243786240 (232.49 GiB 249.64 GB)
>>   Raid Devices : 6
>>  Total Devices : 6
>> Preferred Minor : 0
>>    Persistence : Superblock is persistent
>>
>>    Update Time : Wed Jan 17 23:14:39 2007
>>          State : clean
>> Active Devices : 6
>> Working Devices : 6
>> Failed Devices : 0
>>  Spare Devices : 0
>>
>>         Layout : left-symmetric
>>     Chunk Size : 256K
>>
>>           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
>>         Events : 0.58
>>
>>    Number   Major   Minor   RaidDevice State
>>       0       8        1        0      active sync   /dev/sda1
>>       1       8       17        1      active sync   /dev/sdb1
>>       2       8       33        2      active sync   /dev/sdc1
>>       3       8       49        3      active sync   /dev/sdd1
>>       4       8       65        4      active sync   /dev/sde1
>>       5       8       81        5      active sync   /dev/sdf1
>> [root@compaq ~]#
>>
>>
>> Sevrin 

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

Re: bad performance on RAID 5

[dean gaudet]

On Wed, 17 Jan 2007, Sevrin Robstad wrote:

> I'm suffering from bad performance on my RAID5.
> 
> a "echo check >/sys/block/md0/md/sync_action"
> 
> gives a speed at only about 5000K/sec , and HIGH load average :
> 
> # uptime
> 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52

iostat -kx /dev/sd? 10  ... and sum up the total IO... 

also try increasing sync_speed_min/max....

and a loadavg jump like that suggests to me you have other things 
competing for the disk at the same time as the "check".

-dean

RE: bad performance on RAID 5

[Roger Lucas]

Hi Sevrin,

Are you sure all the disks are working OK?

We saw a problem here with a 4-disk SATA array.  The array was working
without errors but was _very_ slow.  When we checked each disk individually,
we found one disk was reporting SMART errors and running slow.  We removed
it and replaced it with a new disk and the RAID array ran at full speed
again.  Further tests on the removed disk found that it was having a lot of
problems but just about hanging in there (although taking a long time for
each operation) - hence the RAID array didn't mark it as faulty.

I would check the SMART logs with smartctl to see if anything looks a bit
wrong and try benchmarking the disks individually too.

- Roger

Re: bad performance on RAID 5

[Nix]

On 18 Jan 2007, Bill Davidsen spake thusly:
> ) Steve Cousins wrote:
>> time dd if=/dev/zero of=/mount-point/test.dat bs=1024k count=1024
> That doesn't give valid (repeatable) results due to caching issues. Go
> back to the thread I started on RAID-5 write, and see my results. More
> important, the way I got rid of the cache effects (beside an unloaded
> systems) was:
>  sync; time bash -c "dd if=/dev/zero bs=1024k count=2048 of=/mnt/point/file; sync"
> I empty the cache, then time the dd including the sync at the
> end. Results are far more repeatable.

Recent versions of dd have `oflag=direct' as well, to open the output
with O_DIRECT. (I'm not sure what the state of O_DIRECT on regular files
is though.)

-- 
`The serial comma, however, is correct and proper, and abandoning it will
surely lead to chaos, anarchy, rioting in the streets, the Terrorists
taking over, and possibly the complete collapse of Human Civilization.'

Re: bad performance on RAID 5

[Bill Davidsen]

Nix wrote:
> On 18 Jan 2007, Bill Davidsen spake thusly:
>   
>> ) Steve Cousins wrote:
>>     
>>> time dd if=/dev/zero of=/mount-point/test.dat bs=1024k count=1024
>>>       
>> That doesn't give valid (repeatable) results due to caching issues. Go
>> back to the thread I started on RAID-5 write, and see my results. More
>> important, the way I got rid of the cache effects (beside an unloaded
>> systems) was:
>>  sync; time bash -c "dd if=/dev/zero bs=1024k count=2048 of=/mnt/point/file; sync"
>> I empty the cache, then time the dd including the sync at the
>> end. Results are far more repeatable.
>>     
>
> Recent versions of dd have `oflag=direct' as well, to open the output
> with O_DIRECT. (I'm not sure what the state of O_DIRECT on regular files
> is though.)
>
>   
Doing the write using page cache and then just a single sync at the end 
gives a closer estimate of what can be written to the array in general. 
By going to O_DIRECT every i/o take place unbuffered, which is more 
typical of database use or similar. My original problem was capturing 
real data at 75MB/s and not being able to write it to an array that 
fast, taking advantage of page cache. By going to huge stripe cache, 
about 20x larger than default, performance was boosted to a more useful 
level.

I think both measurements are useful, but they aren't measuring the same 
thing.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979