zfs discuss - Jul 2010 - zvol recordsize for backing a zpool over iSCSI

Just wondering if anyone has experimented with working out the best zvol 
recordsize for a zvol which is backing a zpool over iSCSI?

-- 
Andrew Gabriel

On Jul 30, 2010, at 11:35 AM, Andrew Gabriel wrote:
> Just wondering if anyone has experimented with working out the best zvol
recordsize for a zvol which is backing a zpool over iSCSI?

This is an interesting question.  Today, most ZFS implementations are done
directly on devices with an effective, fixed recordsize of 512 bytes.  But that
isn''t very efficient and things like raidz don''t quite work
like you might expect.
Next up is 4KB sectors, which is a better starting point, IMHO.

That said, ultimately it is the size of the data to be written that dictates the
best answer.

-- 
Richard Elling
richard at nexenta.com   +1-760-896-4422
Enterprise class storage for everyone
www.nexenta.com

On 2-8-2010 2:53, Richard Elling wrote:
> On Jul 30, 2010, at 11:35 AM, Andrew Gabriel wrote:
>
>   
>> Just wondering if anyone has experimented with working out the best
zvol recordsize for a zvol which is backing a zpool over iSCSI?
>>     
>
> This is an interesting question.  Today, most ZFS implementations are done
> directly on devices with an effective, fixed recordsize of 512 bytes.  But
that
> isn''t very efficient and things like raidz don''t quite
work like you might expect.
> Next up is 4KB sectors, which is a better starting point, IMHO.
>
> That said, ultimately it is the size of the data to be written that
dictates the
> best answer.
>
>   
Up to now i configure the recordsize of a iscsi zvol to match the same
as the one seen by the iscsi initiator side.
So for instance if i''m creating an iscsi zvol for a NTFS volume ,
depending on the size of the zvol, i use from 4KB up to 64KB as seen in
http://support.microsoft.com/?scid=kb%3Ben-us%3B140365&x=20&y=18 .
Likewise if i''m going to use an EXT3 filesystem i try to use the same
rules, as seen in http://en.wikipedia.org/wiki/Ext3#Size_limits .

This has been working good for me, but probably i''m not the best
example
since i "refuse" to provide iscsi zvol''s on RAIDn
implementations, i
only use ZFS Mirrors for that..

Bruno

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.