On Tue, Nov 10, 2009 at 9:15 AM, Robin Hill <robin@xxxxxxxxxxxxxxx> wrote: > On Tue Nov 10, 2009 at 07:01:02PM +0300, Majed B. wrote: > >> Which disks can provide 2ms response with a read of 250 MB/s and write >> of 170 MB/s other than SSDs?! >> >> Are you saying that it doesn't matter whether we use Linux or Windows >> with SSDs because the limitation is coming from the disk's controller >> itself? >> > Not exactly - without TRIM support, the drive performance will degrade > over time. Not true. First, it never effects read performance (you didn't qualify). Given that SSD's have a management layer that rotating media doesn't, it is a very complex issue, and dependent on the SSD management layer's algorithms. For many of these algorithms, most typical write usage performance is completely unaffected. The biggest performance effect is seen in benchmarks that were designed w/ rotating media in mind that makes assumptions that don't apply to real applications, but given rotating media's simplicity were justifiable. Those assumptions are no longer justifiable given SSD's management layer; benchmarks must be re-coded to exhibit more application-like behavior. > Windows 7 has TRIM implemented for deletes (and formats), > which prevents this degradation. Initial performance will be the same > on both systems though (as performance is limited by the interface - > SATA 6G is starting to appear though, which will definitely help). > > Currently, AFAIK, none of the Linux filesystems support TRIM. ext4 supports discard. I've been using successfully since 2.6.27. FAT did too, but it was pulled. > This is > largely due to discussions about the implementation - a TRIM call > requires a full flush of all pending writes (as it's a non-queueable > call) which results in severe performance issues if done synchronously > on deletes. This only causes performance issues for ill-designed SSD's that put themselves behind legacy controllers for compatibility reasons. Conceptually, for SSS, the earlier the TRIM the better (the sooner the management layer can use that information), no matter the perceived fragmentation. The performance issue only arises with the poor compatibility design, but, given they are the loudest voices in the Linux community, their design will prevail. Chris > > HTH, > Robin > -- > ___ > ( ' } | Robin Hill <robin@xxxxxxxxxxxxxxx> | > / / ) | Little Jim says .... | > // !! | "He fallen in de water !!" | > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
