ext3 with maildir++ = huge disk latency and high load

[Eric Sandeen]

On 9/23/11 9:43 AM, Eric Sandeen wrote:
> On 9/23/11 4:52 AM, Andrey wrote:
>> Thank you for reply,
>>
>> BTW, other webserver has almost the same bonnie results (10283ms and
>> 5884ms) on ext3 partition with 45GB of data (1.5 millions of
>> files)?!
>>
>> Hardware and RAID5(also hardware) are the same: HP Proliant DL380 G4
>> with SmartArray 6i controller (as I see it comes with 128MB BBWC
>> enabler but not kit).
>>
>> I did not tried to mount fs with barriers disabled. Does it have any
>> crititcal risks?
> 
> Yes.  If you have write caches on either the raid controller or on
> the disks behind it which can be lost on a power outage, running
> without barriers will potentially corrupt your filesystem if you lose
> power, even though you have ext3's journaling.
> 
> Journaling depends on write guarantees which are lost if drive
> write caches evaporate.

... evaporate unexpectedly that is.  barriers manage that cache.

If write caches are battery-backed (or off), then nobarrier is safe.

-Eric
 
> -Eric