On Wed, Mar 7, 2012 at 2:54 AM, Joel Jacobson <joel@trustly.com> wrote:
> My company is in the process of migrating to a new pair of servers, running 9.1.
>
> The database performance monetary transactions, we require
> synchronous_commit on for all transactions.
>
> Fusion-io is being considered, but will it give any significant
> performance gain compared to normal SATA-based SSD-disks, due to the
> fact we must replicate synchronously?
>
> To make it more complicated, what about SLC vs MLC (for synchronous
> replication)?
>
> Assume optimal conditions, both servers have less than a meter between
> each other, with the best possible network link between them providing
> the lowest latency possible, maxed out RAM, maxed out CPUs, etc.
>
> I've already asked this question to one of the core members, but the
> answer was basically "you will have to test", I was therefore hoping
> someone in the community already had some test results to avoid
> wasting money.
>
> Thank you for any advice!
flash, just like hard drives, has some odd physical characteristics
that impose some performance constraints, especially when writing, and
double especially when MLC flash is used. modern flash drives employ
non volatile buffers to work around these constraints that work pretty
well *most* of the time. since MLC is much cheaper improvements in
flash controller technology are basically pushing SLC out of the
market except in high end applications.
if you need zero latency storage all the time and are willing to spend
the extra bucks, then pci-e based SLC is definitely worth looking at
(you'll have another product to evaluate soon when the intel 720
ramsdale hits the market). a decent MLC drive might work for you
though, i'd suggest testing there first and upgrading to the expensive
proprietary stuff if and only if you really need it.
my experience with flash and postgres is that even with low-mid range
drives like the intel 320 it's quite a challenge to make postgres be
i/o bound.
merlin
