On 07/18/2013 06:55 PM, John R Pierce wrote:
> and not all Intel drives have the key features of supercap backed cache,
> and reliable write-acknowlegement behavior you want from a server.
Regardless of your storage, your system should be powered by a monitored
UPS. Verify that it works, and the drive's cache shouldn't be a major
concern.
> that 95% (20:1) only applies to a SSD compared with a single desktop
> grade (7200rpm) disk.
>
> do note, you can easily build proper SAS raids that are just about as
> fast as a single SSD when used for write intensive database OTLP
Yes, but an array can be built with SSDs as well. Its performance will
have the same advantage over the SAS array that an SSD has over a single
drive.
> one funny thing I've noted about various SSD's. when they are new,
> they benchmark much faster than after they've been in production use.
> expect a several times slowdown in write performance once you've written
> approximately the size of the disk worth of blocks. NEVER let them
> get above about 75% full.
Again, yes, but that's what TRIM is for. The slowdown you noticed is
the result of using a filesystem or array that didn't support TRIM.
My understanding is that some of the current generation of drives no
longer need TRIM. The wear-leveling and block remapping features
already present were combined with a percentage of reserved blocks to
automatically reset blocks as they're re-written. I couldn't name those
drives, though.
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