On 5/24/2013 12:15 PM, keld@xxxxxxxxxx wrote: > On Fri, May 24, 2013 at 02:37:01AM -0500, Stan Hoeppner wrote: >> On 5/24/2013 1:32 AM, keld@xxxxxxxxxx wrote: >>> On Thu, May 23, 2013 at 10:45:56PM -0500, Stan Hoeppner wrote: >>>> On 5/23/2013 3:30 AM, keld@xxxxxxxxxx wrote: >>>>> On Thu, May 23, 2013 at 12:59:39AM -0500, Stan Hoeppner wrote: >>>> >>>>>> You may be tempted to use md/RAID10 of some layout >>>>>> to optimize for writes, but you'd gain nothing, and you'd lose some >>>>>> performance due to overhead. The partitions you'll be using in this >>>>>> case are so small that they easily fit in a single physical disk track, >>>>>> thus no head movement is required to seek between sectors, only rotation >>>>>> of the platter. >>>> ... >>>>> I think a raid10,far3 is a good choice for swap, then you will enjoy >>>>> RAID0-like reading speed. and good write speed (compared to raid6), >>>>> and a chance of live surviving if just one drive keeps functioning. >>>> >>>> As I mention above, none of the md/RAID10 layouts will yield any added >>>> performance benefit for swap partitions. And I state the reason why. >>>> If you think about this for a moment you should reach the same conclusion. >>> >>> I think it is you who are not fully aquainted with Linux MD. Linux >>> MD RAID10,far3 offers improved performance in single read, >> >> On most of today's systems, read performance is largely irrelevant WRT >> swap performance. However write performance is critical. None of the >> md/RAID10 layouts are going to increase write throughput over RAID1 >> pairs. And all the mirrored RAIDs will be 2x slower than interleaved >> swap across direct disk partitions. > > In my experience read performance from swap is critical, at least > on single user systems. Eg swapping in firefox or libreoffice > may take quite some time and there raid10,far helps by almost halfing > the time for the swapping in. writes are not important, as long as you are not trashing. If a single user system has multiple drives configured in RAID10 and productivity applications are being swapped, then the user should be smacked in the head. 2GB DIMMs are $10. Any hard drive is $50+ but usually much more. This is not a valid argument. > In general halfing the swapping in with raid10,far is nice for a process, but > for small processes it is not noticable for a laptop user or a > server user, say http or ftp. Neither is this. Laptop users don't run RAID10. And server swap performance is all about page write, not read, as I previously stated. -- Stan -- 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
