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've tested MD1000,
MD1200, and MD1220 arrays before, and always gotten seriously good
performance relative to the dollars spent with that series. Only one of
these Dell storage arrays I've heard two disappointing results from (but
not tested directly yet) is the MD3220.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
