Re: SSD slowdown with 3.3.X?

[Stan Hoeppner <stan@hardwarefreak.com>]

On 4/23/2012 7:44 AM, Mark Lord wrote:
> On 12-04-21 02:30 PM, Stan Hoeppner wrote:
>> On 4/21/2012 6:45 AM, cwillu wrote:
>>>> Probably not relevant in this case but maybe worth mentioning to get the
>>>> word out:
>>>>
>>>> "As of kernel 3.2.12, the default i/o scheduler, CFQ, will defeat much
>>>> of the parallelization in XFS."
>>>>
>>>> http://www.xfs.org/index.php/XFS_FAQ
>>>
>>> Not that it's terribly relevant to btrfs, but do you have a better
>>> citation for that than a very recent one-line wiki change that only
>>> cites the user's own anecdote?
>>
>> Apologies for the rather weak citation.  It was simply easier to quote
>> that wiki entry.
>>
>> How about something directly from Dave's fingers:
>> http://www.spinics.net/lists/xfs/msg10824.html
>>
>> The many issues with CFQ+XFS didn't start with 3.2.12, but long before that.
> 
> 
> Thanks for the link.  That's handy to know.
> 
> The problems there are for XFS+RAID vs. CFQ, not XFS by itself.
> Enterprise servers will normally have RAID under XFS,
> but not all smaller systems.

While it's true there are single disk XFS filesystems in the wild--I
have one--I'd have to make an educated guess that the vast majority of
XFS filesystems reside atop SAN, HBA, or md based RAID.  For any
hardware RAID solution with write cache, noop is recommended allowing
the hardware scheduler to order the writes, since they're sitting in his
cache.  For md based RAID I believe most are getting best results with
deadline.

I can't quote any numbers as I don't believe anyone has done such a poll
or research on this.  So it's best guess only.

-- 
Stan