Re: [zfs-discuss] Sudden drop in disk performance - WD20EURS & 4k sectors to blame?

2011-08-16 Thread krad 
On 15 August 2011 15:55, Andrew Gabriel  wrote:

> David Wragg wrote:
>
>> I've not done anything different this time from when I created the
>> original (512b)  pool. How would I check ashift?
>>
>>
>
> For a zpool called "export"...
>
> # zdb export | grep ashift
> ashift: 12
> ^C
> #
>
> As far as I know (although I don't have any WD's), all the current 4k
> sectorsize hard drives claim to be 512b sectorsize, so if you didn't do
> anything special, you'll probably have ashift=9.
>
> I would look at a zpool iostat -v to see what the IOPS rate is (you may
> have bottomed out on that), and I would also work out average transfer size
> (although that alone doesn't necessarily tell you much - a dtrace quantize
> aggregation would be better). Also check service times on the disks (iostat)
> to see if there's one which is significantly worse and might be going bad.
>
> --
> Andrew Gabriel
>
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from what i have read you really do need to 4k align your drives and
ashift=12 them on the western digitals. Unfortunately that probably means
you have to rebuild your pool. 4k aligining is fairly easy it just means
when you partition a disk, just make sure the 1st sector and the size of
the partition is /8. Ie dont start the 1st partition at sector 34 as
normally happens, start it at say 40. eg here are my 4k alinged drives from
a freebsd system

# gpart show ada0
=>34  3907029101  ada0  GPT  (1.8T)
  34   6- free -  (3.0k)
  40 128 1  freebsd-boot  (64k)
 168 6291456 2  freebsd-swap  (3.0G)
 6291624  3900213229 3  freebsd-zfs  (1.8T)


making ashift=12 is a little more tricky. I have seen a patch posted on the
mailing lists for zpool which forces it. Alternatively you could boot into a
freebsd live cd and create the pool with the 'gnop -S 4096' trick. Its
possible there is another way to do it now on opensolaris that i havent
come across yet
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Re: [zfs-discuss] Sudden drop in disk performance - WD20EURS & 4k sectors to blame?

2011-08-15 Thread Andrew Gabriel 

David Wragg wrote:

I've not done anything different this time from when I created the original 
(512b)  pool. How would I check ashift?
  


For a zpool called "export"...

# zdb export | grep ashift
ashift: 12
^C
#

As far as I know (although I don't have any WD's), all the current 4k 
sectorsize hard drives claim to be 512b sectorsize, so if you didn't do 
anything special, you'll probably have ashift=9.


I would look at a zpool iostat -v to see what the IOPS rate is (you may 
have bottomed out on that), and I would also work out average transfer 
size (although that alone doesn't necessarily tell you much - a dtrace 
quantize aggregation would be better). Also check service times on the 
disks (iostat) to see if there's one which is significantly worse and 
might be going bad.


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Andrew Gabriel
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Re: [zfs-discuss] Sudden drop in disk performance - WD20EURS & 4k sectors to blame?

2011-08-15 Thread David Wragg 
I've not done anything different this time from when I created the original 
(512b)  pool. How would I check ashift?
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Re: [zfs-discuss] Sudden drop in disk performance - WD20EURS & 4k sectors to blame?

2011-08-15 Thread chris scott 
Did you 4k align your partition table and is ashift=12?
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