On 3/14/2013 3:37 PM, Mark Kirkwood wrote:
I not convinced about the need for BBU with SSD - you *can* use them without one, just need to make sure about suitable longevity and also the presence of (proven) power off protection (as discussed previously). It is worth noting that using unproven or SSD known to be lacking power off protection with a BBU will *not* save you from massive corruption (or device failure) upon unexpected power loss.
I think it probably depends on the specifics of the deployment, but for us the fact that the BBU isn't required in order to achieve high write tps with SSDs is one of the key benefits -- the power, cooling and space savings over even a few servers are significant. In our case we only have one or two drives per server so no need for fancy drive string arrangements.
Also, in terms of performance, the faster PCIe SSD do about as well by themselves as connected to a RAID card with BBU. In fact they will do better in some cases (the faster SSD can get close to the max IOPS many RAID cards can handle...so more than a couple of 'em plugged into one card will be throttled by its limitations).
You might want to evaluate the performance you can achieve with a single-SSD (use several for capacity by all means) before considering a RAID card + SSD solution.
Again I bet it depends on the application but our experience with the older Intel 710 series is that their performance out-runs the CPU, at least under our PG workload.