[CentOS] RAID6 in production?

[Joshua Baker-LePain]

On Thu, 20 Oct 2005 at 9:43am, Aleksandar Milivojevic wrote

> Quoting Joshua Baker-LePain <jlb17 at duke.edu>:
>
>> Needless to say it's not giving me that warm fuzzy feeling.  The one caveat 
>> is that not all the members of my array were the same size -- one disk is 
>> 180GB while all the rest are 160GB.  I'm going to test overnight with 
>> identically sized RAID members, but I also wanted to see if anyone else is 
>> using RAID6.
>
> I was testing RAID-5 with identical disk drives.  Got the same thing.  If I
> attempt to access it while it rebuilds, sooner or later I get errors.  If I
> reboot while it rebuilds, it doesn't start it after the reboot (forgot the
> actuall error message).  I needed to manually kick it again using mdadm to
> force-start it.  If it was root file system, the machine would probably fail 
> to
> boot completely.  You might want to stick to your 3ware for now.

Wonderful.  I'm testing RAID5 now, for which I had high hopes.

> BTW, any particular reason not to use hardware RAID on 3ware?

That was the initial plan.  But I can't get anything even resembling 
decent speeds out of them.  These systems have 2 7500-8 boards in 'em (on 
separate PCI buses).  I had been running RH7.3 (!!) and XFS with the 
boards in hardware RAID5 and a software RAID0 stripe across those, and 
would get >100MB/s writes and >300MB/s reads.  With centos-4 and ext3, I 
was getting ~30MB/s writes and ~200MB/s reads.  The reads I'd be OK with, 
but the write speed is absurd.  I tweaked all I could think of, but 
nothing helped much.

-- 
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University