On Tue, Nov 10, 2009 at 6:51 PM, George Janczuk < geor...@objectconsulting.com.au> wrote:
> I've been following the use of SSD with ZFS and HSPs for some time now, and > I am working (in an architectural capacity) with one of our IT guys to set > up our own ZFS HSP (using a J4200 connected to an X2270). > > The best practice seems to be to use an Intel X25-M for the L2ARC > (Readzilla) and an Intel X25-E for the ZIL/SLOG (Logzilla). > > However, whilst being a BIG thing in the Windows 7 world - I have pretty > much heard nothing about Intel's G2 devices and updated firmware when > Intel's SSDs are used in a ZFS HSP. In particular, does ZFS use or support > the TRIM command? Is it even relevant or useful in a hierarchical (vs. > primary) storage context? > > Any comment would be appreciated. Some comment from the Fishworks guys in > particular would be great! > > My personal thought would be that it doesn't really make sense to even have it, at least for readzilla. In theory, you always want the SSD to be full, or nearly full, as it's a cache. The whole point of TRIM, from my understanding, is to speed up the drive by zeroing out unused blocks so they next time you try to write to them, they don't have to be cleared, then written to. When dealing with a cache, there shouldn't (again in theory) be any free blocks, a warmed cache should be full of data. Logzilla is kind of in the same boat, it should constantly be filling and emptying as new data comes in. I'd imagine the TRIM would just add unnecessary overhead. It could in theory help there by zeroing out blocks ahead of time before a new batch of writes come in if you have a period of little I/O. My thought is it would be far more work than it's worth, but I'll let the coders decide that one. --Tim
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