Re: [zfs-discuss] ZFS Hard disk buffer at 100%

[Giovanni Tirloni]

On Fri, May 7, 2010 at 8:07 AM, Emily Grettel <emilygrettelisnow@xxxxxxxxxxx> wrote:

Hi,
 
I've had my RAIDz volume working well on SNV_131 but it has come to my attention that there has been some read issues with the drives. Previously I thought this was a CIFS problem but I'm noticing that when transfering files or uncompressing some fairly large 7z (1-2Gb) files (or even smaller rar - 200-300Mb) files occasionally running iostat will give the b% as 100 for a drive or two.

That's the percent of time the disk is busy (transactions in progress) - iostat(1M).

 

 
I have the Western Digital EADS 1TB drives (Green ones) and not the more expensive black or enterprise drives (our sysadmins fault).
 
The pool in question spans 4x 1TB drives.
 
What exactly does this mean? Is it a controller problem disk problem or cable problem? I've got this on commodity hardware as its only used for a small business with 4-5 staff accessing our media server. Its using the Intel ICHR SATA controller. I've already changed the cables, swapped out the odd drive that exhibted this issue and the only thing I can think of is to buy a Intel or LSI SATA card.
 
The scrub sessions take almost a day and a half now (previously at most 12hours!) but theres also 70% of space being used (files wise they're chunky MPG files) or compressed artwork but there are no errors reported.
 
Does anyone have any ideas?

You might be maxing out your drives' I/O capacity. That could happen when ZFS is commting the transactions to disk every 30 seconds but if %b is constantly high you disks might not be keeping up with the performance requirements.

We've had some servers showing high asvc_t times but it turned out to be a firmware issue in the disk controller. It was very erratic (1-2 drives out of 24 would show that).

If you look in the archives, people have sent a few averaged I/O performance numbers that you could compare to your workload.

-- 
Giovanni

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