On Sat, Jun 18, 2005 at 06:42:27PM +0200, Yves Vindevogel wrote:
With striping, each file is distributed over several disks, making the physical write faster because several disks can do the work. Same for reading, multiple disks return a part of the file.
A mirror behaves almost exactly the same for reads, with a caveat: for a large enough file, multiple disks *must* be accessed in a striped configuration, while in a mirrored configuration the controller may access either one or more disks to read any file.
BTW: mirroring is always slower than striping.
That's simply not true. Striping speeds up writes but has no advantage over a simlarly sized mirror for reading. In fact, the mirror will be faster for pathological cases in which the reads are aligned in such a way that they would all be have to be read from the same stripe of a striped array. The striped configuration has an advantage when more than two disks are used, but that derives from the number of spindles, not from the striping; it is possible to have a mirror of more than two disks (which would have the same read advantage as the striped configuration with the same number of disks) but this is rarely seen because it is expensive. Mike Stone ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org