Slow raid10 resync

Slow raid10 resync

[Ryan_MichaelS]

Occasionally one of my devices with a 4 drive raid10 array resyncs very
slowly.  Typical resync speed is in the 50-60 MB/sec range.  When
running slow the speed is around 7-10 MB/sec.  sync_speed_min is set to
20,000, max is set to 200,000.  By setting sync_speed_min to 5000 I can
slow the sync further, but setting it back to 20000 doesn't fix the
speed.  Other IO on the system is normal.  The drives and the CPU are
not maxed.

I don't know what is triggering this slow sync state.  Once in this
state it will continue until the build completes.

Any idea what might be happening here?  I'm running Debian with a 2.6.22
kernel.

Thanks for your help.
- Michael

Re: Slow raid10 resync

[Sujit Karataparambil]

I think this is the max performance you can get,
but that is only the software raid.

http://tldp.org/HOWTO/Software-RAID-HOWTO-9.html
http://linux-raid.osdl.org/index.php/Performance

better guide that I thought would be helpfull, but did see some
activity on the mailing list.


On Mon, Jun 22, 2009 at 11:04 PM, <Ryan_MichaelS@emc.com> wrote:
> Occasionally one of my devices with a 4 drive raid10 array resyncs very
> slowly.  Typical resync speed is in the 50-60 MB/sec range.  When
> running slow the speed is around 7-10 MB/sec.  sync_speed_min is set to
> 20,000, max is set to 200,000.  By setting sync_speed_min to 5000 I can
> slow the sync further, but setting it back to 20000 doesn't fix the
> speed.  Other IO on the system is normal.  The drives and the CPU are
> not maxed.
>
> I don't know what is triggering this slow sync state.  Once in this
> state it will continue until the build completes.
>
> Any idea what might be happening here?  I'm running Debian with a 2.6.22
> kernel.
>
> Thanks for your help.
> - Michael
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Re: Slow raid10 resync

[Neil Brown]

On Monday June 22, Ryan_MichaelS@emc.com wrote:
> Occasionally one of my devices with a 4 drive raid10 array resyncs very
> slowly.  Typical resync speed is in the 50-60 MB/sec range.  When
> running slow the speed is around 7-10 MB/sec.  sync_speed_min is set to
> 20,000, max is set to 200,000.  By setting sync_speed_min to 5000 I can
> slow the sync further, but setting it back to 20000 doesn't fix the
> speed.  Other IO on the system is normal.  The drives and the CPU are
> not maxed.
> 
> I don't know what is triggering this slow sync state.  Once in this
> state it will continue until the build completes.
> 
> Any idea what might be happening here?  I'm running Debian with a 2.6.22
> kernel.

Not really...
There have been a couple of bugs that cause resync to go faster than
it should, but I can't think of anything that would make it go slower
than sync_speed_min unless that the the fastest that the storage
subsystem could handle.

Is this just a default raid10 with 'near=2' as the layout?

NeilBrown

RE: Slow raid10 resync

[Ryan_MichaelS]

>On Monday June 22, Ryan_MichaelS@emc.com wrote:
> Occasionally one of my devices with a 4 drive raid10 array resyncs
very
>> slowly.  Typical resync speed is in the 50-60 MB/sec range.  When
>> running slow the speed is around 7-10 MB/sec.  sync_speed_min is set
to
>> 20,000, max is set to 200,000.  By setting sync_speed_min to 5000 I
can
>> slow the sync further, but setting it back to 20000 doesn't fix the
>> speed.  Other IO on the system is normal.  The drives and the CPU are
>> not maxed.
>> 
>> I don't know what is triggering this slow sync state.  Once in this
>> state it will continue until the build completes.
>> 
>> Any idea what might be happening here?  I'm running Debian with a
2.6.22
>> kernel.
>
> Not really...
> There have been a couple of bugs that cause resync to go faster than
> ..it should, but I can't think of anything that would make it go
slower
> than sync_speed_min unless that the the fastest that the storage
> subsystem could handle.
>
> Is this just a default raid10 with 'near=2' as the layout?
>
> NeilBrown

Yep, default raid12, near=2.  The device can handle 50-60 MB/sec.  When
the resync is running slow there doesn't seem to be anything else on the
system that is consuming CPU or IO resources.

Thanks for the info, I'll keep digging.
- Michael