really strange ext4 behavior

Michał Piotrowski mkkp4x4 at gmail.com
Sun Feb 13 18:45:17 UTC 2011


W dniu 13 lutego 2011 19:29 użytkownik Dennis Jacobfeuerborn
<dennisml at conversis.de> napisał:
> On 02/12/2011 11:52 PM, Ric Wheeler wrote:
>>
>> On 02/12/2011 05:31 PM, Michał Piotrowski wrote:
>>>
>>> Hi,
>>>
>>> W dniu 12 lutego 2011 23:19 użytkownik Ric Wheeler
>>> <rwheeler at redhat.com>   napisał:
>>>>
>>>> On 02/12/2011 05:12 PM, Michał Piotrowski wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I added a disc to my box. I wanted to use ext4. I run fs_mark to test
>>>>> speed, to my surprise I heard a really strange noises.
>>>>>
>>>>> It's very strange because the drive is new
>>>>>    9 Power_On_Hours          0x0032   100   100   000    Old_age
>>>>> Always       -       12
>>>>>
>>>>>
>>>>> #  fs_mark  -d  test/
>>>>> [..]
>>>>> FSUse%        Count         Size    Files/sec     App Overhead
>>>>>       0         1000        51200         22.8            54347
>>>>>
>>>>> I decided to create an ext3 file system on this drive and everything
>>>>> works
>>>>> fine.
>>>>>
>>>>> #  fs_mark  -d  test/
>>>>> [..]
>>>>> FSUse%        Count         Size    Files/sec     App Overhead
>>>>>       0         1000        51200        103.7            57229
>>>>>
>>>>> When I mount this ext3 fs as ext4 and run fs_mark I hear strange sounds
>>>>> again.
>>>>>
>>>>> I use F14 and self compiled kernel from rawhide 2.6.37-1.fc14.x86_64 +
>>>>> e2fsprogs-1.41.14-2.fc14.x86_64.
>>>>>
>>>>> I mount ecryptfs on top of this file system.
>>>>>
>>>>> Does anyone know what might be causing this strange ext4 behavior?
>>>>>
>>>> Hi Michael,
>>>>
>>>> fs_mark run a fsync heavy test. What you might be hearing is the impact
>>>> of
>>>> the fsync's. ext4 defaults to using "write barriers" enabled, ext3 does
>>>> not.
>>>> Without write barriers, those fsync push data from the box to the write
>>>> cache on the drive only. With barriers, the disk will flush that cache
>>>> to
>>>> the platter, so the platter moves and you probably hear the head, etc.
>>>>
>>>> You can test if this is the cause by mouting ext4 with "nobarrier" to
>>>> see if
>>>> the noise goes away.
>>>
>>> I mounted fs with nobarrier and now it works just like ext3. Thanks! This
>>> solves
>>> the riddle :)
>>>
>>
>> Good to hear that it worked!
>>
>> Note that the barrier code makes your data safer, so you should run with
>> it on
>> by default (unless you really don't care about the file system).
>
> If ext3 was running fine without barriers for all these years why is this
> such a problem with ext4? Does ext4 do something differently that barriers
> are now required?

Ext4 uses extents - AFAIRC it is harder to recover data on file system
that uses extents, so perhaps for this reason additional measures were
taken

>
> Regards,
>  Dennis
>



-- 
Best regards,
Michal

http://eventhorizon.pl/


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