On 25 July, 2011 - Erik Trimble sent me these 2,0K bytes: > On 7/25/2011 3:32 AM, Orvar Korvar wrote: >> How long have you been using a SSD? Do you see any performance decrease? I >> mean, ZFS does not support TRIM, so I wonder about long term effects... > > Frankly, for the kind of use that ZFS puts on a SSD, TRIM makes no > impact whatsoever. > > TRIM is primarily useful for low-volume changes - that is, for a > filesystem that generally has few deletes over time (i.e. rate of change > is low). > > Using a SSD as a ZIL or L2ARC device puts a very high write load on the > device (even as an L2ARC, there is a considerably higher write load than > a "typical" filesystem use). SSDs in such a configuration can't really > make use of TRIM, and depend on the internal SSD controller block > re-allocation algorithms to improve block layout. > > Now, if you're using the SSD as primary media (i.e. in place of a Hard > Drive), there is a possibility that TRIM could help. I honestly can't > be sure that it would help, however, as ZFS's Copy-on-Write nature means > that it tends to write entire pages of blocks, rather than just small > blocks. Which is fine from the SSD's standpoint.
You still need the flash erase cycle. > On a related note: I've been using a OCZ Vertex 2 as my primary drive > in a laptop, which runs Windows XP (no TRIM support). I haven't noticed > any dropoff in performance in the year its be in service. I'm doing > typical productivity laptop-ish things (no compiling, etc.), so it > appears that the internal SSD controller is more than smart enough to > compensate even without TRIM. > > > Honestly, I think TRIM isn't really useful for anyone. It took too long > to get pushed out to the OSes, and the SSD vendors seem to have just > compensated by making a smarter controller able to do better > reallocation. Which, to me, is the better ideal, in any case. Bullshit. I just got a OCZ Vertex 3, and the first fill was 450-500MB/s. Second and sequent fills are at half that speed. I'm quite confident that it's due to the flash erase cycle that's needed, and if stuff can be TRIM:ed (and thus flash erased as well), speed would be regained. Overwriting an previously used block requires a flash erase, and if that can be done in the background when the timing is not critical instead of just before you can actually write the block you want, performance will increase. /Tomas -- Tomas Ögren, st...@acc.umu.se, http://www.acc.umu.se/~stric/ `- Sysadmin at {cs,acc}.umu.se _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
