[OmniOS-discuss] iSCSI poor write performance

[Steffen Wagner]

Hi Hanno,

how do you calculate the best ashift value?

Thanks,
Steffen

-----Original Message-----
From: OmniOS-discuss [mailto:omnios-discuss-bounces at lists.omniti.com] On Behalf Of Hanno Hirschberger
Sent: Mittwoch, 23. September 2015 14:43
To: omnios-discuss at lists.omniti.com
Subject: Re: [OmniOS-discuss] iSCSI poor write performance

Hi Martin,

On 23.09.2015 10:51, Martin Truhlář wrote:
> Tests revealed, that problem is somewhere in disk array itself.

are you familiar with the ashift problem on 4k drives? My best guess 
would be that the 1 TB WD drives are emulating a block size of 512 bytes 
while using 4k sectors internally. OmniOS is using a ashift value of 9 
then to align the data efficiently (on 512 byte sectors!). This slows 
the whole pool down - I had the same problem before. The ashift value 
has to be 12 on 4k drives!

Try the command 'zdb' to gather the values for your drives. Look for 
'ashift: 9' oder 'ashift: 12'.

Regards,

Hanno
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