David Brown wrote:
However, AFAIUI, you are wrong about TRIM being essential for the continued high performance of SSDs. As long as your SSDs have some over-provisioning (or you only partition something like 90% of the drive), and it's got good garbage collection, then TRIM will have minimal effect.
I beg to differ. We are using SSDs in very much the way that Tom de Mulder intends, and from our extensive performance measurements over many months now I can say that (at least if you do have significant amounts of write operations) it _does_ make a lot of difference whether you periodically discard the unused sectors or not. (For us, the write performance measured to be about half as good when there are no free erase blocks available anymore.) Of course, you can only benefit from discards if your filesystem is not full (because then there is nothing to discard). But any kind of "garbage collection" by the SSD itself will not have the same effect, since it cannot know which blocks are in use by the filesystem.
I think other SSD-optimisations, such as those in BTRFS, are much more important.
Actually, (apart from btrfs still being in development, not really ready for production use, yet), XFS (-o delaylog,barrier) performs better on our SSDs than btrfs - without any SSD-specific options. What is really an important factor for SSD performance: The controller. The same SSDs perform with significantly lower latency for us when connected to SATA controller channels than when connected to SAS controllers (and they perform abysmal when used as hardware-RAID constituents, in comparison). Regards, Lutz Vieweg -- 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
