I was today reasearching this same phenomenon.
The multipath is required for HA storage solutions with redundant i/o path
backplanes and redundant controllers.
( If a controller fails, the other one can still access the harddisk.)
I read about an LSI SAS-to-SATA bridge what can be attacched onto an
ordinary SATA
drive to make it operate like a SAS drive (e.g. be able to multi path to
that drive.)
Is there anyone on the list that can give some information about this?
I am google-ing my pants of to find some kind of shop selling these bridges.
I want to build a redundant JBOD to share between two ZFS
hosts.(Active/Standby)
I already found the nearline SAS disks, but this will not fix the multipath
problem for SATA SSD disks.
Regards,
Armand
----- Original Message -----
From: "Erik Trimble" <erik.trim...@sun.com>
To: "Tim Cook" <t...@cook.ms>
Cc: "zfs-discuss" <zfs-discuss@opensolaris.org>
Sent: Tuesday, January 19, 2010 8:06 AM
Subject: Re: [zfs-discuss] "NearLine SAS"?
Tim Cook wrote:
On Tue, Jan 19, 2010 at 12:16 AM, Erik Trimble <erik.trim...@sun.com
<mailto:erik.trim...@sun.com>> wrote:
A poster in another forum mentioned that Seagate (and Hitachi,
amongst others) is now selling something labeled as "NearLine SAS"
storage (e.g. Seagate's NL35 series).
Is it me, or does this look like nothing more than their standard
7200-rpm enterprise drives with a SAS or FC interface instead of a
SATA one?
I can't see any real advantage of those over the existing
enterprise SATA drives (e.g. Seagate's Constellation ES series),
other than not needing a FC/SAS->SATA gateway in the external
drive enclosure.
Seagate claims the SAS versions of their drives actually see IOPS
improvements:
http://www.seagate.com/www/en-us/products/servers/barracuda_es/barracuda_es.2
If the SAS version is dual ported like I would expect, that's also a
MAJOR benefit.
--
--Tim
stupid question here: I understand the advantages of dual-porting a drive
with a FC interface, but for SAS, exactly what are the advantages other
than being able to read and write simultaneously (obviously, only from the
on-drive cache).
And yeah, these Seagates are dual-ported SAS. (according to the spec
sheet)
Also, a 38% increase in IOPS without LESS drive cache seems unlikely. Or,
at least highly workload-dependent.
Check that, they're claiming 38% better IOPS/watt over the SATA version,
which, given that the SAS one pulls 10% more watts, means in absolute
terms 45% or so. I'm really skeptical that only an interface change can
do that.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
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