I recently bought two Intel 320 80GB SSDs and plan to use them on a Fedora 16 system for boot/root, home and other frequently used data. I planned to mirror them together using md raid/Linux software RAID for reliability, and use LVM to partition. I did some investigation on insuring data alignment for best performance, etc. along with verification that my criteria for setting them up could be met: 1) must be mirrored since SSDs are similar to hard drives in their reliability (i.e. lack of) 2) must support passing TRIM commands through the RAID layer (e.g. ext4- >LVM->RAID->SSD) to avoid write amplification that reduces SSD lifetime and performance 3) ideally should maximize performance by splitting reads between both SSDs Unfortunately, my investigation determined that while both md raid and dmraid/fakeraid can of course accomplish #1, only dmraid does #2 and only md raid does #3! At first it looked like I had to give up #3, but I think I have a way around this dilemma, at the cost of a bit of additional complexity which I'm totally comfortable with. My plan is to use dmraid/ICH10R to create two equal sized RAID-1 volumes, with the primary mirror of the first volume as sda and the primary mirror of the second volume as sdb, then create all my LVM volumes by striping extents from the two dmraid devices. Am I correct that this will meet my criteria? Does anyone see another method that avoids dmraid? If md raid handled TRIM it would be my preference since I've used it before and have no need to dual boot with Windows, but I guess its not ready yet. Any gotchas to my solution I need to worry about which I may be overlooking? Thanks for any tips or suggestions! PS - its too bad you can't set the 'strip size' parameter for RAID 1 in dmraid and have it swap its idea of "primary mirror" on each stripe. Not sure if the Intel metadata format would allow storing that value for a RAID 1 volume, but if it does this would be a way to avoid having all reads directed at one drive. While there may be some good reasons to avoid indiscriminately splitting reads between hard drives, with SSDs the algorithm doesn't need much intelligence to see a major performance boost... -- Douglas Siebert douglas-siebert@xxxxxxxxx -- 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
