Messages in this thread | | | Date | Wed, 09 Jun 1999 20:42:52 +0000 | From | Paul Doom <> | Subject | Re: Byte blasts Linux? |
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> > I always thought that Linux striped through all configured swap > > partitions, and I didn't need to do swap over RAID. In fact, if I > > remember well, the documentation of the Raid tools says that swapping > > over a striped device won't give better performance, because the kernel > > already stripes swap partitions... > > Well, you certainly want to put the swap space on the RAID array because > otherwise, you are doomed if one of your drives blows up. ;)
Linux only writes swap evenly accross multiple disks (stripe) if you set the swap priority of each swap partition to an equal value. If one is set higher than another (which is what swapon defaults to doing if you do not specify priorities), then you get the same effect as in using the "linear" (also called "append") type md driver, where the kernel only writes to one swap partition till said partition is full, then it writes to the next, following the swap priorities. See the swapon man page for details. Using a RAID 0 device for swap instead of using multiple swap partitions may or may not be a win. Using RAID 0 will lose on overhead to direct swap, but since you can tune the stripe size on a RAID device, it might come out ahead with certain hardware. (I would be interested to see this tested.) Using swap on RAID levels other than 0 may be of use to some for fault tolerance.
-Paul
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