Extreme slowness with xfs [WAS: Re: Slowness with new pc]

[Eric Sandeen]

Stian Jordet wrote:
> ti., 25.11.2008 kl. 01.09 +0100, skrev Sven-Haegar Koch:
>> I had the same problem when I tried it on my laptop (T60) - using it on 
>> the unencrypted root filesystem (with /usr/src) took ages, using it on 
>> the LUKS encrypted /home was blasing fast - on the same disk.
>>
>> This test was some time ago with something like 2.6.20 or 2.6.24 - I 
>> gave up and reformatted / with ext3 as I needed the machine.
>>
>> I think barriers were the problem, they seem to cost performance like 
>> hell, especially for operations with many small files. My laptop used 
>> barriers for xfs on the direct partition, but not on crypto drivermapper 
>> mounts.
>>
>> So perhaps try mounting with nobarrier and see if the speed problem goes 
>> away - but know that you sacrifice some crash-resilience when doing so.
> 
> Barriers were the problem indeed. My old system had no problems with
> barriers, but here it did an incredible difference.

Depending on the old system, perhaps its storage did not allow the
barriers to be honored, so after xfs saw a test barrier write fail at
mount time, it disabled them ... you'd see a message if that were the
case, FWIW.

-Eric