> -----Original Message----- > From: zfs-discuss-boun...@opensolaris.org > [mailto:zfs-discuss-boun...@opensolaris.org] On Behalf Of Miles Nordin > Sent: Tuesday, October 12, 2010 5:15 PM > To: zfs-discuss@opensolaris.org > Subject: Re: [zfs-discuss] Bursty writes - why? > > >>>>> "en" == Eff Norwood <sm...@jsvp.com> writes: > > en> We also tried SSDs as the ZIL which worked ok until they got > en> full, then performance tanked. As I have posted before, SSDs > en> as your ZIL - don't do it! > > yeah, iirc the thread went back and forth between you and I for a few > days, something like this, > > you: SSD's work fine at first, then slow down, see this anandtech > article. We got bit by this. > > me: That article is two years old. Read this other article which is > one year old and explains the problem is fixed if you > buy current gen2 > intel or sandforce-based SSD. > > you: Well absent test results from you I think we will just have to > continue believing that all SSD's gradually slow down like I > said, though I would love to be proved wrong. > > me: You haven't provided any test results yourself nor even said what > drive you're using. We've both just cited anandtech, and my > citation's newer than yours. > > you: I welcome further tests that prove the DDRDrive is not the only > suitable ZIL, but absent these tests we have to assume I'm right > that it is. > > silly! > > slowdowns with age: > http://www.pcper.com/article.php?aid=669 > http://www.anandtech.com/show/2738/15 > > slowdowns fixed: > http://www.anandtech.com/show/2899/8 > > ``With the X25-M G2 Intel managed to virtually eliminate the > random-write performance penalty on a sequentially filled > drive. In other words, if you used an X25-M G2 as a normal desktop > drive, 4KB random write performance wouldnC"BB > http://www.anandtech.com/show/2738/25 t really degrade over > time. Even without TRIM.'' > > note this is not advice to buy sandforce for slog because I don't > know if anyone's tested it respects flush-cache commands and suspect > it may drop them. > > sumary: There's probably been major, documented shifts in the industry > between when you tested and now, but no one knows because you don't > even tell what you tested or how---you just spread FUD and flog the > DDRDrive and then say ``do research to prove me wrong or else my hazy > statement stands.'' bad science.
Another article concerning Sandforce performance: http://www.anandtech.com/show/3667/6 Evidently, since the Sandforce controllers do deduplication to reduce writes, write performance with highly random data suffers relative to 'normal' data. In particular: "Sequential write speed actually takes the biggest hit of them all. At only 144.4MB/s if you're writing highly random data sequentially you'll find that the SF-1200/SF-1500 performs worse than just about any other SSD controller on the market. Only the X25-M is slower. While the impact to read performance and random write performance isn't terrible, sequential performance does take a significant hit on these SandForce drives." Unfortunately, this article doesn't actually compare performance for writes of random data between different controllers, it just says that the random data write performance of the Sandforce is worse than everything but the X25-M relative to their 'normal' data write performance. Do other controllers do dedup on written data like Sandforce? When I read this I thought that it kind of eliminated Sandforce drives from consideration as SLOG devices, which is a pity because the OCZ Vertex 2 EX or Vertex 2 Pro SAS otherwise look like good candidates. -Will _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
