linux-kernel - Re: Problem with shared interrupt latency with a RAID6 array?

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Date:	Fri, 24 Dec 2010 16:19:07 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Grant Coady <gcoady.lk@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Problem with shared interrupt latency with a RAID6 array?

On 12/22/2010 05:57 AM, Grant Coady wrote:
> Hi there,
>
> Built my first RAID6 array with 5 x 1TB SATA drives.
>
> I notice this odd number in the SMART values for the last two drives on the
> array.  The drives connect to an Intel ICH9R chip, the mobo has a 2.13GHz
> Core2Duo CPU and 4GB memory, running Slackware64-13.1 with 2.6.36.2a kernel.
>
> While feeding data into the array from a USB 2.0 attached drive, the box's
> load average was about 3.5, the box was very responsive and I transferred
> over 900GB into the RAID6 array.
>
> The fourth and fifth drives report lots of command timeouts in the SMART
> data.  Is this a problem?
>
> Is it because the drives share an interrupt?
>
> Extract from dmesg:
>
> root@...h:~# egrep -e '^(ahci|ata)' /var/log/dmesg
> ahci 0000:00:1f.2: version 3.0
> ahci 0000:00:1f.2: PCI INT B ->  GSI 19 (level, low) ->  IRQ 19
> ahci 0000:00:1f.2: irq 40 for MSI/MSI-X
> ahci: SSS flag set, parallel bus scan disabled
> ahci 0000:00:1f.2: AHCI 0001.0200 32 slots 6 ports 3 Gbps 0x3f impl SATA mode
> ahci 0000:00:1f.2: flags: 64bit ncq sntf stag pm led clo pmp pio slum part ccc ems
> ahci 0000:00:1f.2: setting latency timer to 64
> ata1: SATA max UDMA/133 abar m2048@...6386000 port 0xf6386100 irq 40
> ata2: SATA max UDMA/133 abar m2048@...6386000 port 0xf6386180 irq 40
> ata3: SATA max UDMA/133 abar m2048@...6386000 port 0xf6386200 irq 40
> ata4: SATA max UDMA/133 abar m2048@...6386000 port 0xf6386280 irq 40
> ata5: SATA max UDMA/133 abar m2048@...6386000 port 0xf6386300 irq 40
> ata6: SATA max UDMA/133 abar m2048@...6386000 port 0xf6386380 irq 40
> ata7: PATA max UDMA/100 cmd 0xc000 ctl 0xc100 bmdma 0xc400 irq 16
> ata8: PATA max UDMA/100 cmd 0xc200 ctl 0xc300 bmdma 0xc408 irq 16
> ata7.00: ATAPI: PIONEER DVD-RW  DVR-110D, 1.41, max UDMA/66
> ata7.00: configured for UDMA/66
> ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
> ata1.00: ATA-8: ST31000528AS, CC46, max UDMA/133
> ata1.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 31/32)
> ata1.00: configured for UDMA/133
> ata2: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
> ata2.00: ATA-8: ST31000528AS, CC46, max UDMA/133
> ata2.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 31/32)
> ata2.00: configured for UDMA/133
> ata3: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
> ata3.00: ATA-8: ST31000528AS, CC46, max UDMA/133
> ata3.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 31/32)
> ata3.00: configured for UDMA/133
> ata4: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
> ata4.00: ATA-8: ST31000528AS, CC46, max UDMA/133
> ata4.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 31/32)
> ata4.00: configured for UDMA/133
> ata5: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
> ata5.00: ATA-8: ST31000528AS, CC46, max UDMA/133
> ata5.00: 1953525168 sectors, multi 0: LBA48 NCQ (depth 31/32)
> ata5.00: configured for UDMA/133
> ata6: SATA link down (SStatus 0 SControl 300)
>
> And here's SMART's command timeout numbers:
>
> root@...h:~# for d in a b c d e; do smartctl -a /dev/sd${d} |grep Command_Timeout; done
> 188 Command_Timeout         0x0032   100   100   000    Old_age   Always       -       0
> 188 Command_Timeout         0x0032   100   100   000    Old_age   Always       -       0
> 188 Command_Timeout         0x0032   100   100   000    Old_age   Always       -       0
> 188 Command_Timeout         0x0032   100   100   000    Old_age   Always       -       65537
> 188 Command_Timeout         0x0032   100   100   000    Old_age   Always       -       65537
>
> Is this a problem?  Is there something I can change in the .config?

Well, if it is a problem it's presumably hardware related. Are those 
command timeout numbers increasing? If so, then you might look at 
anything that might be common to those two drives - things like having 
too many hard drives on one power cable coming from the power supply 
have caused drive problems for some people in the past. In some cases 
power supply problems can occur when running multiple hard drives in a 
machine, especially in a RAID configuration where all drives are likely 
to be accessed at once.

>
> Config and full dmesg are at:
>
>    http://bugsplatter.id.au/kernel/boxen/pooh/config-2.6.36.2a.gz
>    http://bugsplatter.id.au/kernel/boxen/pooh/dmesg-2.6.36.2a.gz
>
> Ask, and I'll provide more info, do tests and so on.
>
> Could this issue be related to RAID6 unreliability reports one finds for
> some Linux based NAS devices on the 'net?
>
> Thanks,
> Grant.

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