really strange ext4 behavior

Michał Piotrowski mkkp4x4 at gmail.com
Sat Feb 12 22:31:41 UTC 2011


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 :)

>
> Drives can be noisy, but occasionally, if they are over noisy (you hear
> chattering when writing), it might just be a bad drive that has trouble
> settling the heads after a seek.
>
> You might want to check with:
>
>  smartctl -a /dev/sda
>
> To look for errors that the drive reports.

I regularly test all drives that I use, this one is irreproachable

  1 Raw_Read_Error_Rate     0x002f   200   200   051    Pre-fail
Always       -       0

[..]

Num  Test_Description    Status                  Remaining
LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed without error       00%        10         -


>
> Good luck!
>
> Ric
>
>

Thanks for your help!

-- 
Best regards,
Michal

http://eventhorizon.pl/


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