Stephen Liu wrote: > Apart from using a software RAID card connected to HDs, I never use > Linux/FC/RH software RAID before. I'm interested to have a test. > Please help me to understand > > 1) > Do I need 2 HDs for RAID 0/1/2? RAID 2 is hardly ever used. Do you mean RAID 5? RAID 0 has no redundancy -- you use two hard disks (ideally the same size) and the system "stripes" the data across them to make a virtual disk that's twice as large as one physical hard disk. If one disk goes wrong, you lose everything on the drive. RAID 1 (mirroring) writes two copies of everything, one to each of two drives. If one drive goes wrong, you have a complete copy of everything on the other. RAID 5 needs at least three disks. It stripes user data and "parity" across them in such a way that if one disk goes down, you can use the data and parity on the other two disks to get back your data. You get (in this case) the equivalent of two disks' worth of space. See http://en.wikipedia.org/wiki/RAID for more details. > 2) > If 1) above be "YES", whether both of them have to be connected as > master on primary IDE and Secondary IDE respectively. No: they can be wherever you want as long as Linux can see them. Note that having two heavily-used devices on the same IDE channel will degrade performance. > 3) > Is there a visible improvement on operation in running RAID 0/1/2 Depends what you're doing -- you *may* see an improvement for disk-heavy applications (e.g. opening a Maildir mail archive, or compiling the kernel). Or (especially with RAID 5 and a lot of small writes, e.g. to a large database) you may see *slower* disk performance. Hope this helps, James. -- E-mail address: james | Am I alone in receiving so much junk mail? Can these @westexe.demon.co.uk | people not get it into their thick heads that I do not | *want* a Chinese boat? | Yours sincerely, Mrs Trellis. -- ISIHAC, BBC Radio 4
