Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!cs.utexas.edu!natinst!uudell!bigtex!james From: james@bigtex.cactus.org (James Van Artsdalen) Newsgroups: comp.sys.ibm.pc.hardware Subject: Disk Arrays (Was: ISA boards, EISA bus) Message-ID: <48109@bigtex.cactus.org> Date: 1 Oct 90 00:36:24 GMT References: <1471@gold.GVG.TEK.COM> <1477@gold.GVG.TEK.COM> <5777@holston.UUCP> <1970@sixhub.UUCP> Reply-To: james@bigtex.cactus.org (James Van Artsdalen) Organization: Institute of Applied Cosmology, Austin TX Lines: 35 In <1970@sixhub.UUCP>, davidsen@sixhub.UUCP (bill davidsen) wrote: | In article <5777@holston.UUCP> barton@holston.UUCP (Barton A. Fisk) writes: | The catch is drive failure causes loss of pieces of all files. Compaq | offers several solutions to guard against this including mirroring | and controller duplexing and data guarding. [...] > I can see how that would work using any of several schemes, but all of > them seem to require not using the other drives until the failed unit is > replaced. [...] (Hopefully I didn't take Bill's comments too far out of context) Actually, a key goal of data guarding is to keep running in the event of a failure. For example, with the Dell drive array, you can have a drive completely fail (yank the power cable out) without any errors. This can be any drive, not just one group (ie, nothing magic about the guard drive). I'm not familiar with the Compaq scheme, but I assume they use something similar. The cost of this is one extra drive: if you have N drives of storage capacity, you need N+1 drives to do data guarding with the Dell scheme. But for someone who needs continuous availability, it's pretty useful. Until the defective drive is replaced, there is no data guarding and performance is reduced. When the drive is finally replaced, the array controller will rebuild the drive and go back to full speed and guarding mode. The drive rebuild can be done in "background" while the system is running. Performance is reduced until the rebuild is finished, but the system is fully available. -- James R. Van Artsdalen james@bigtex.cactus.org "Live Free or Die" Dell Computer Co 9505 Arboretum Blvd Austin TX 78759 512-338-8789