Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!always.com!rick From: rick@always.com (Rick Wagner) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Drive Arrays Message-ID: <1991Apr11.185756.3593@always.com> Date: 11 Apr 91 18:57:56 GMT References: <46563@ut-emx.uucp> <1991Apr9.210740.16385@athena.mit.edu> Distribution: na Organization: Always Technology Corp. Lines: 29 In article <1991Apr9.210740.16385@athena.mit.edu> mmshah@athena.mit.edu (Milan M Shah) writes: >>solomon@chaos.utexas.edu (Thomas Solomon) writes: >>Both provide data guarding. On the Dell drive array, your data is >>striped on four disks with a fifth for parity. > >Actually, a better idea is to spread the parity across all drives. ie, parity >for sector 1 is stored on disk 1, for 2 on 2 for 6 back to 1 etc. Even then >you are limited. > The fifth drive is probably not parity, but ECC, allowing for correction of lost data. That way, if one drive goes bad, (think of the array as four data drives, and one ECC drive), if its a data drive, then the ECC corrects the lost data bytes. If it's the ECC drive, then you continue running with just the data. When you get a replacement, the system should reconstruct the new drive from the existing data. Not saying thats what the Dell or Compaq DO, but thats the way I understand some arrays to work. --rick -- =============================================================================== Rick Wagner email: rick@always.COM Always Technology Voice: 1-818-597-1400 31336 Via Colinas, Suite 101 Fax: 1-818-597-1496