I've also looked at the Fusion-IO products. They are not standard
flash drives. They don't appear as SATA devices. They contains an
FPGA that maps the flash directly to the PCI bus. The kernel-mode
drivers blits data to/from them via DMA, not a SATA or SAS drive (that
would limit transfer rates to 6Gb/s).
But, I don't have any in-hand to test with yet... :( But the
kool-aide looks tasty :)
On Thu, Mar 8, 2012 at 8:52 AM, Merlin Moncure <mmoncure@gmail.com> wrote:
> 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
>
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