really strange ext4 behavior
Ric Wheeler
rwheeler at redhat.com
Sat Feb 12 22:19:52 UTC 2011
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.
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.
Good luck!
Ric
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