On 03/08/2010 22:49, Ross Walker wrote:
On Aug 3, 2010, at 12:13 PM, Roch Bourbonnais<roch.bourbonn...@sun.com> wrote:
Le 27 mai 2010 à 07:03, Brent Jones a écrit :
On Wed, May 26, 2010 at 5:08 AM, Matt Connolly
<matt.connolly...@gmail.com> wrote:
I've set up an iScsi volume on OpenSolaris (snv_134) with these commands:
sh-4.0# zfs create rpool/iscsi
sh-4.0# zfs set shareiscsi=on rpool/iscsi
sh-4.0# zfs create -s -V 10g rpool/iscsi/test
The underlying zpool is a mirror of two SATA drives. I'm connecting from a Mac
client with global SAN initiator software, connected via Gigabit LAN. It
connects fine, and I've initialiased a mac format volume on that iScsi volume.
Performance, however, is terribly slow, about 10 times slower than an SMB share
on the same pool. I expected it would be very similar, if not faster than SMB.
Here's my test results copying 3GB data:
iScsi: 44m01s 1.185MB/s
SMB share: 4m27 11.73MB/s
Reading (the same 3GB) is also worse than SMB, but only by a factor of about 3:
iScsi: 4m36 11.34MB/s
SMB share: 1m45 29.81MB/s
<cleaning up some old mail>
Not unexpected. Filesystems have readahead code to prefetch enough to cover the
latency of the read request. iSCSI only responds to the request.
Put a filesystem on top of iscsi and try again.
For writes, iSCSI is synchronous and SMB is not.
It may be with ZFS, but iSCSI is neither synchronous nor asynchronous is is
simply SCSI over IP.
It is the application using the iSCSI protocol that determines whether it is
synchronous, issue a flush after write, or asynchronous, wait until target
flushes.
I think the ZFS developers didn't quite understand that and wanted strict
guidelines like NFS has, but iSCSI doesn't have those, it is a lower level
protocol than NFS is, so they forced guidelines on it and violated the standard.
Nothing has been violated here.
Look for WCE flag in COMSTAR where you can control how a given zvol
should behave (synchronous or asynchronous). Additionally in recent
build you have zfs set sync={disabled|default|always} which also works
with zvols.
So you do have a control over how it is supposed to behave and to make
it nice it is even on per zvol basis.
It is just that the default is synchronous.
--
Robert Milkowski
http://milek.blogspot.com
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