Speeding up resilvering

[Karl Denninger]

On 7/8/2015 09:19, Matthew Seaman wrote:
> On 2015/07/08 14:58, Karl Denninger wrote:
>> On 7/8/2015 08:50, Matthew Seaman wrote:
>>> Hi,
>>>
>>> I've a zpool which is taking an inordinately long time to resilver and
>>> replace a device.  It had only got to about 8% completion after a day,
>>> implying over a week to resilver about 6TB data.
>>>
>>> Now, I've applied the resilver performance tuning sysctls from
>>> https://wiki.freebsd.org/ZFSTuningGuide:
>>>
>>> vfs.zfs.scrub_delay=0
>>> vfs.zfs.top_maxinflight=128
>>> vfs.zfs.resilver_min_time_ms=5000
>>> vfs.zfs.resilver_delay=0
>>>
>>> but it doesn't seem to have made a great deal of difference.  Most of
>>> the benefit there would apparently come from reducing scrub_delay or
>>> resilver_delay -- but this system is only booted to single user mode, so
>>> the drives are otherwise idle and the resilver should have automatically
>>> switched to running full throttle anyhow.
>>>
>>> Given the machine is not going to be doing anything else other than
>>> resilvering for the time being, is there any more aggressive tuning or
>>> tricks to get it to go faster that people would recommend?
>>>
>>> 	Cheers,
>>>
>>> 	Matthew
>>>
>> What OS version?
>>
> 10.1-RELEASE-p10
>
> 	Cheers,
>
> 	Matthew
Look at the IO saturation on the disk channel(s) involved with either
systat -vm or iostat.  If the channel is saturated then there's nothing
you can do in terms of tuning; the question then turns to why actual I/O
performance is so poor and has to be addressed there.

-- 
Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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