Re: Raid5 Construction Question

[PAulN <pauln@psc.edu>]

I have it mounted now but the performance sucks because
the resync is going on.    I've already test each disk individually and 
I get
38MB/sec.  The machine is a 2,.4 GHz xeon with 2GB ram so there should
be no problem with cpu or memory.    Before I tried raid5 i made an 8xraid0
stripe which yielded ~120MB/sec which is what I'd expect from the 
controller.
So there is no way to initialize the raid5 device - similar to what a 
hardware raid
controller does?
p

Guy wrote:

>You don't need to wait.  You can use the array now.
>
>But ouch 305K/sec!  If this a 386-33?  :)
>
>Have you tried dd tests on each disk to verify each works well?
>
>Something like:
>time dd if=/dev/sdc1 of=/dev/null bs=64k count=100000
>This is just a read test.  My disks take about 340 seconds.  Yours should be
>about twice as fast.
>
>Each disk should give about the same performance.
>You may find 1 that has issues.
>
>If you are willing to re-build the array, you could do a write test:
>time dd if=/dev/zero of=/dev/sdc1 bs=64k count=10000
>THIS WILL TRASH THE ARRAY!!!
>
>Guy
>
>-----Original Message-----
>From: linux-raid-owner@vger.kernel.org
>[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of PAulN
>Sent: Thursday, August 19, 2004 1:53 PM
>To: Guy
>Cc: linux-raid@vger.kernel.org
>Subject: Re: Raid5 Construction Question
>
>Guy,
>thanks for the snappy reply!  I wish my disks were as fast :)
>I failed to mention that I had been tweaking those proc values.  Currently
>they are:
>(root@lcn0:raid)# cat speed_limit_max
>200000
>(root@lcn0:raid)# cat speed_limit_min
>10000
>
>If I'm correct, this means that the min speed is 10MB/sec per device.
>I've verified that each device has a seq write speed of about 38MB/sec so
>each should be capable of handling 10,000Kbytes sec.  Right after I issue
>a raidstart the speed is pretty good (~30MB/sec) but is just falls until 
>it hits
>around 300K. 
>
>md0 : active raid5 sdh1[7] sdf1[6] sdg1[5] sde1[4] sdd1[3] sdc1[2] 
>sdb1[1] sda1[0]
>      481949184 blocks level 5, 64k chunk, algorithm 2 [7/7] [UUUUUUU]
>      [>....................]  resync =  2.4% (1936280/80324864) 
>finish=4261.4min speed=305K/sec
>
>In the docs I saw that "reconstruction" is possible with raidhotadd but 
>I didn't
>see anything about initialization.   So am I "screwed" until the resync 
>is fixed?  I was depeding
>on the disks to do some filesystem testing but maybe I'll have to wait a 
>few days.. 
>Thanks,
>Paul
>
>
>Guy wrote:
>
>  
>
>>In short... Issue this command:
>>echo 100000 > /proc/sys/dev/raid/speed_limit_max
>>
>>If it does not help issue this command and send the results:
>>cat /proc/mdstat
>>
>>Details below.
>>
>>These are related to throttling:
>>/proc/sys/dev/raid/speed_limit_max
>>/proc/sys/dev/raid/speed_limit_min
>>
>>Do "man md" for more info.
>>
>>The speed limits are per device, not per array.
>>Make sure the max is large enough the permit your disks to go as fast as
>>they can.  I use 100000 (100,000K bytes/second).  My disks are not that
>>fast, and having too large of a number does not hurt.
>>At least as a test, set the min to the same value as max.
>>
>>I use these commands when I want to change by hand:
>>cat /proc/sys/dev/raid/speed_limit_max
>>cat /proc/sys/dev/raid/speed_limit_min
>>
>>echo 100000 > /proc/sys/dev/raid/speed_limit_max
>>echo 1000 > /proc/sys/dev/raid/speed_limit_min
>>
>>Guy
>>
>>-----Original Message-----
>>From: linux-raid-owner@vger.kernel.org
>>[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of PAulN
>>Sent: Thursday, August 19, 2004 1:25 PM
>>To: linux-raid@vger.kernel.org
>>Subject: Raid5 Construction Question
>>
>>Hi,
>>So I have a raid 5 which is around ~1TB and the problem I've been having 
>>is that
>>the resync rate is really bad.  This is understandable given that the 
>>raid5 has not
>>been initialized.  Does anyone know a way for me to initialize my raid5 
>>before I use it so
>>that the resync process doesn't run for 3 days?
>>thanks
>>paul
>>
>>
>>Config:
>>-------------------------------------------------
>>raiddev             /dev/md0
>>raid-level                  5
>>nr-raid-disks               7
>>nr-spare-disks              1
>>chunk-size                  64k
>>persistent-superblock       1
>>parity-algorithm        left-symmetric
>>   device          /dev/sda1
>>   raid-disk     0
>>   device          /dev/sdb1
>>   raid-disk     1
>>   device          /dev/sdc1
>>   raid-disk     2
>>   device          /dev/sdd1
>>   raid-disk     3
>>   device          /dev/sde1
>>   raid-disk     4
>>   device          /dev/sdg1
>>   raid-disk     5
>>   device          /dev/sdf1
>>   raid-disk    6
>>   device          /dev/sdh1
>>   spare-disk     0
>>----------------------------------------
>>
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>>
>>    
>>
>
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