* Posts by dB.in.Oz

1 post • joined 13 Feb 2013

Cache 'n' carry: What's the best config for your SSD?

dB.in.Oz

Re: Make your Own

I'm running an intel S3700 200GB SSD with a 2TB WD Red, setup as a Fusion drive in this late '09 iMac. It makes a huge improvement in speed and boots ~5 seconds after the logo. The SDD replaces the optical drive, which only has a SATA II interface on the MoBo.

A month prior to the 'S3700 I installed an OCZ Vertex 4 - it was a disaster..... The OCZ was fast, but couldn't cope (at all) with our regular power outages. We're in the country and we're lucky if we can go for a week without copping an outage. Even after a re-install with a non-Fusion setup, with the SSD configured as the boot drive, after one outage the SSD completely lost its brain and the machine wouldn't boot! This is a machine that has survived countless power outages over its >3 year life (configured with a HD) with no known data corruption...

Yes, a UPS would help, and I'm repairing some very nice sine-wave units rescued from a dumpster, but the OCZ SSD was so flaky that I couldn't risk kicking the power cord - I expect I'd lose data or down time (it's a business machine). Yes, it is backed up on the hour.

I had a play with ZFS (http://getgreenbytes.com/solutions/zevo/) but it doesn't support time-machine and the can't boot from ZFS.

My theory re OCZ power outage flakiness is that the relatively large RAM caches required in all SSDs (to extend service life and improve performance), combined with background wear-leveling and pretty ordinary firmware, means they're very susceptible to (unexpected) power loss. They probably fare much better in laptops than desktops, as the lappy battery provide a UPS-like function.

It seems only the enterprise grade drives are designed to properly cope with power loss; they all have some form of hold-up capacitance, with power loss detection, to give the on-board controller enough time and energy to dump the RAM contents to flash, so they can recover gracefully next power on. The cost of the capacitors and associated circuitry is quite low. IMHO all >2.5" form factor drives with enough room for the circuitry.

The model new iMac (with the damn screen held on with tape - ARGGHHHH) can be order with SSDs (Sammy 830 series apparently). Assuming these consumer level SSDs don't have on-board capacitors, it may be the MoBo, power supply and firmware support some form of early power-fail detect to allow orderly power-down of the SSD. If not, I can't see these imacs being too reliable..

I realise the 'S700 may sound like complete overkill given the price, but it claims to have consistent performance (see http://www.storagereview.com/reviews/enterprise/ssd) and a good life expectancy, so I expect to able to transfer it to a new machine in a couple of years.

FYI: After the OCA nonsense, I've hammered the intel SSD configuration; intentionally pulled the power numerous times and saw no data corruption whatsoever, well, according to disk util and the general imac happiness..

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