On 7/15/2011 2:10 AM, Greg Smith wrote:
chris wrote:
My employer is a university with little funds and we have to find a
cheap way to scale for the next 3 years, so the SAN seems a good chance
to us.
A SAN is rarely ever the cheapest way to scale anything; you're paying
extra for reliability instead.
I was thinking to put the WAL and the indexes on the local disks, and
the rest on the SAN. If funds allow, we might downgrade the disks to
SATA and add a 50 GB SATA SSD for the WAL (SAS/SATA mixup not possible).
If you want to keep the bulk of the data on the SAN, this is a
reasonable way to go, performance-wise. But be aware that losing the
WAL means your database is likely corrupted. That means that much of
the reliability benefit of the SAN is lost in this configuration.
Any experiences with iSCSI vs. Fibre
Channel for SANs and PostgreSQL? If the SAN setup sucks, do you see a
cheap alternative how to connect as many as 16 x 2TB disks as DAS?
I've never heard anyone recommend iSCSI if you care at all about
performance, while FC works fine for this sort of job. The physical
dimensions of 3.5" drives makes getting 16 of them in one reasonably
sized enclosure normally just out of reach. But a Dell PowerVault
MD1000 will give you 15 x 2TB as inexpensively as possible in a single
3U space (well, as cheaply as you want to go--you might build your own
giant box cheaper but I wouldn't recommend ).
I'm curious what people think of these:
http://www.pc-pitstop.com/sas_cables_enclosures/scsase166g.asp
I currently have my database on two of these and for my purpose they
seem to be fine and are quite a bit less expensive than the Dell
MD1000. I actually have three more of the 3G versions with expanders
for mass storage arrays (RAID0) and haven't had any issues with them in
the three years I've had them.
Bob
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