Strange raid behaviour

[Christian Motta]

After seeing many of these threads I compared what my server tested at 
(mounted)
and now I am concerned about my own results.

My raid is raid 1 w/ 2 300gb Western Digital SATA/7200/8 hard drives

# /sbin/hdparm -t /dev/md4

/dev/md4:
 Timing buffered disk reads:  172 MB in  3.00 seconds =  57.32 MB/sec

so if I am reading this correctly my hard drives are half the speed of 
my nic card????

Is that correct?

-chris




Chris Eborn wrote:

>On 12/15/05, Gilboa Davara <gilboada at netvision.net.il> wrote:
>  
>
>>On Thu, 2005-12-15 at 17:07 +0000, Chris Eborn wrote:
>>    
>>
>>>Does the output from the following  commands seem odd to people?
>>>
>>>[root at nucoda root]# hdparm -t /dev/md0
>>>
>>>/dev/md0:
>>> Timing buffered disk reads:  774 MB in  3.01 seconds = 257.52 MB/sec
>>>[root at nucoda root]# mount /dev/md0 /array
>>>[root at nucoda root]# hdparm -t /dev/md0
>>>
>>>/dev/md0:
>>> Timing buffered disk reads:  416 MB in  3.00 seconds = 138.55 MB/sec
>>>[root at nucoda root]# umount /array
>>>[root at nucoda root]# hdparm -t /dev/md0
>>>
>>>/dev/md0:
>>> Timing buffered disk reads:  776 MB in  3.01 seconds = 257.42 MB/sec
>>>[root at nucoda root]#
>>>
>>>
>>>Tha array is made of 10 scsi disks - each of which will read at around
>>>60 MB/sec and all seems fine with the raid
>>>device until the fs is mounted and it appears to halve the trasnfer
>>>rate! There is no activity in the filesystem. At the moment this
>>>is with FC2, though I have tried with FC3 and numerous kernels.
>>>Tweaking around with block sizes and thing does change the speed of
>>>the raw /dev/md0 -  but the speed always drops when I mount the
>>>filesystem. Can anybody explain this behaviour?
>>>Maybe I am missing something obvious, but this is baffling me - and
>>>what is worse is that it all worked until I upgraded the system. I
>>>have tried to go back, even put a new system disk in and started from
>>>scratch, but cannot get a decent read speed from the array.
>>>
>>>Chris
>>>
>>>      
>>>
>>I'm seeing the same behavior on my 4x36GB MD5 setup.
>>Mounted FS: ~105-110MB/s.
>>Unmount FS: ~125MB/s.
>>
>>Can you check the read-ahead settings (blockdev --getra /dev/md0)
>>before /and/ after fs mount?
>>
>>Gilboa
>>
>>    
>>
>
>Hi There,
>Well I am still suffering with this - I have installed Fedora Core 2
>with kernel 2.6.14 and the raid is still going half speed.
>I have spent quite a while playing with the readahead values (blockdev
>--setra) on both the individual disks and the raid device (/dev/md0)
>and they do not seem to change anything, even with extreme values
>(like "blockdev --setra 0 /dev/sd[abcdefghi]"). Leads me to think that
>readahead has been disabled elsewhere.
>
>Chris
>ps - Unfortunately this machine needs to be able to show 24 12 meg
>files a second (that's because film runs at 24fps) - so come the new
>year it may well have to fall into the windows empire :-(
>
>  
>
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