chunk size.

chunk size.

[jshankar]

For raid devices, i have observed that if size of bytes written is greater 
than the chunk size the read,write performance decreases.For size lesser than 
the chunk size the performance improves.

Please let me know your opinion.


Thanks
Jay

Chunk Size

[Rolf Schatzmann]

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Hi,

I have been using Linux Software Raid 5 for years, it is excellent. If 
anyone involved in the development of it is ever in Perth Australia look 
me up and i will buy you many beers.
Last year i switched from using pata to sata, to be honest it did not 
result in the performance gains I was hoping for and when a drive fails 
it sometimes crashes the host machine (at least with a 2.4 kernel) but 
otherwise its just as dependable as pata raid 5 was. I used to just use 
raid for the data volume of the server but recently i am using it for / 
with a separate raid 1 partition for /boot , it works very well.

In the past I have had to do a few crazy things with raidreconf and got 
away with most of them, however that was when i was using raidtools2 and 
now its all mdadm instead, so my question is this, is there anyway to 
change the chunk size on an existing raid 5 partition without destroying 
the data on it and whilst it is mounted at / .  Yeah you read that 
right, I am laughing too, but I just wanted to be sure i am not missing 
something obvious here, I have in the past found huge performance gains 
by using larger chunk sizes for big file copies and would like to 
experiment.

Thanks in advance!

-- 
--------------------------

Rolf Schatzmann
MacTherapy Australia Pty Ltd
Fax 08 9444 2560
Mobile 0410 577664

We love GNU/Linux Debian.

Http://www.mactherapy.com


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chunk size

[CoolCold]

Hello!
I've assembled two raid1 arrays yesterday, and forgot what chunk size
i've specified. Trying to determine this with mdadm -D /dev/md2 but
have no success, reading man didn't help too. How i can get this info?

bandb:~# mdadm -D /dev/md2
/dev/md2:
        Version : 00.90.03
  Creation Time : Wed Apr  1 05:29:59 2009
     Raid Level : raid1
     Array Size : 290720192 (277.25 GiB 297.70 GB)
    Device Size : 290720192 (277.25 GiB 297.70 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Thu Apr  2 12:51:26 2009
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           UUID : 70a701e2:02c0ab22:6973a307:dc8d6229 (local to host
bandb.blabla.ru)
         Events : 0.6

    Number   Major   Minor   RaidDevice State
       0       8        3        0      active sync   /dev/sda3
       1       8       19        1      active sync   /dev/sdb3


os - debian etch
bandb:~# uname -a
Linux bandb.blabla.ru 2.6.25-2-amd64 #1 SMP Wed May 14 14:04:05 UTC
2008 x86_64 GNU/Linux
bandb:~# mdadm --version
mdadm - v2.5.6 - 9 November 2006

--
--
Best regards,
[COOLCOLD-RIPN]

Re: chunk size

[NeilBrown]

On Thu, April 2, 2009 7:57 pm, CoolCold wrote:
> Hello!
> I've assembled two raid1 arrays yesterday, and forgot what chunk size
> i've specified. Trying to determine this with mdadm -D /dev/md2 but
> have no success, reading man didn't help too. How i can get this info?
>
> bandb:~# mdadm -D /dev/md2
> /dev/md2:
>         Version : 00.90.03
>   Creation Time : Wed Apr  1 05:29:59 2009
>      Raid Level : raid1

Chunksize has no meaning on a RAID1.

NeilBrown


>      Array Size : 290720192 (277.25 GiB 297.70 GB)
>     Device Size : 290720192 (277.25 GiB 297.70 GB)
>    Raid Devices : 2
>   Total Devices : 2
> Preferred Minor : 2
>     Persistence : Superblock is persistent
>
>     Update Time : Thu Apr  2 12:51:26 2009
>           State : clean
>  Active Devices : 2
> Working Devices : 2
>  Failed Devices : 0
>   Spare Devices : 0
>
>            UUID : 70a701e2:02c0ab22:6973a307:dc8d6229 (local to host
> bandb.blabla.ru)
>          Events : 0.6
>
>     Number   Major   Minor   RaidDevice State
>        0       8        3        0      active sync   /dev/sda3
>        1       8       19        1      active sync   /dev/sdb3
>
>
> os - debian etch
> bandb:~# uname -a
> Linux bandb.blabla.ru 2.6.25-2-amd64 #1 SMP Wed May 14 14:04:05 UTC
> 2008 x86_64 GNU/Linux
> bandb:~# mdadm --version
> mdadm - v2.5.6 - 9 November 2006
>
> --
> --
> Best regards,
> [COOLCOLD-RIPN]
> --
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