Date:	Tue, 08 Jan 2008 18:00:50 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Guillaume Laurès <guillaume-laures@...f.fr>
Cc:	linux-kernel@...r.kernel.org, ide <linux-ide@...r.kernel.org>
Subject: Re: PROBLEM: I/O scheduler problem with an 8 SATA disks raid 5 under
 heavy load  ?



Guillaume Laurès wrote:
> 
> Le 8 janv. 08 à 01:29, Robert Hancock a écrit :
> 
>> From your report:
>>
>> ata5: EH in ADMA mode, notifier 0x0 notifier_error 0x0 gen_ctl 
>> 0x1501000 status 0x400
>> ata5: CPB 0: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 1: ctl_flags 0x1f, resp_flags 0x2
>> ata5: CPB 2: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 3: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 4: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 5: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 6: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 7: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 8: ctl_flags 0x1f, resp_flags 0x2
>> ata5: CPB 9: ctl_flags 0x1f, resp_flags 0x2
>> ata5: CPB 10: ctl_flags 0x1f, resp_flags 0x2
>> ata5: CPB 11: ctl_flags 0x1f, resp_flags 0x2
>> ata5: CPB 12: ctl_flags 0x1f, resp_flags 0x2
>> ata5: CPB 13: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 14: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 15: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 16: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 17: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 18: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 19: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 20: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 21: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 22: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 23: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 24: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 25: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 26: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 27: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 28: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 29: ctl_flags 0x1f, resp_flags 0x1
>> ata5: CPB 30: ctl_flags 0x1f, resp_flags 0x1
>> ata5: Resetting port
>> ata5.00: exception Emask 0x0 SAct 0x1f02 SErr 0x0 action 0x2 frozen
>> ata5.00: cmd 60/40:08:8f:eb:67/00:00:03:00:00/40 tag 1 cdb 0x0 data 
>> 32768 in
>>          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>> ata5.00: cmd 60/08:40:17:eb:67/00:00:03:00:00/40 tag 8 cdb 0x0 data 
>> 4096 in
>>          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>> ata5.00: cmd 60/18:48:47:eb:67/00:00:03:00:00/40 tag 9 cdb 0x0 data 
>> 12288 in
>>          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>> ata5.00: cmd 60/08:50:77:eb:67/00:00:03:00:00/40 tag 10 cdb 0x0 data 
>> 4096 in
>>          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>> ata5.00: cmd 60/08:58:87:eb:67/00:00:03:00:00/40 tag 11 cdb 0x0 data 
>> 4096 in
>>          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>> ata5.00: cmd 60/48:60:d7:eb:67/00:00:03:00:00/40 tag 12 cdb 0x0 data 
>> 36864 in
>>          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
>> ata5: soft resetting port
>>
>> The CPB resp_flags 0x2 entries are ones where the drive has been sent 
>> the request and the controller is waiting for a response. The timeout 
>> is 30 seconds, so that means the drive failed to service those queued 
>> commands for that length of time.
>>
>> It may be that your drive has a poor NCQ implementation that can 
>> starve some of the pending commands for a long time under heavy load?
> 
> Thanks for your answer. That could very well be the problem, as all 4 
> drives on the sata_nv HBA are older than the sata_sil ones.
> I'm going to swap them to see if the problem is reproducible on the 
> sata_sil HBA. (see test #2)
> 
> - Test #1
> I switched the scheduler to CFQ on all disks and ran the file 
> reorganizer all night. In the morning I ended with a drive missing in 
> the array. And lots of SATA port resets, with plenty of 0x2 again, see 
> the attached log.

> BTW, you can see around "md2: recovery done" a second disk failed before the first was completely rebuilt.
> 
> 
> 
> - Test #2
> 
> I swapped all the drives with this scheme: sda->sdh, sdb->sdg, sdc->sdf,..., sdg->sdb, sdh->sda. So now all the newer drives are attached through sata_nv (ata5:8), the oldest through sata_sil (ata1:4)
> 
> I kept the scheduler to anticipatory and ran xfs_frs. 60 seconds later it hanged. Still on ata5/ata6, i.e. sata_nv. Drive reconstruction...
> 
> Then I switched the scheduler to CFQ. xfs_fsr + 10 seconds: another freeze. No drive loss from the array though. See the dmesg below.
> 
> ------------------------------------------------------------------------
> 
> So it seems to be either a cabling problem or a bug with sata_nv ? I'm running gentoo's 2.6.20-xen, and maybe my problem looks like the sata_nv/adma/samsung problems reports I can see on the net ?
> 

I don't think it's the same problem. In that case the controller appears 
to indicate that it didn't even start processing the command. In this 
case it's indicating that the command was sent to the drive and is still 
waiting for it to indicate completion.

It could be a cabling problem, yes. Also, are you sure your power supply 
is able to handle the power draw of that many drives?
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