On Fri, 06 Apr 2007 19:47:36 PDT, [email protected] said: > On Fri, 6 Apr 2007 11:21:19 -0400, "Jan Harkes" <[email protected]> > > With compression there is a pretty high probability that one corrupted > > byte or disk block will result in loss of a considerably larger amount > > of data. > > Bad blocks are NOT dealt with by the filesystem,... so your comment is > irrelevant, or just plain wrong. > > If your filesystem is writing to bad blocks, then throw away your > operating system. You know... occasionally, blocks go bad *after* you write to them. If you have an uncompressed filesystem, it's often possible to recover most of the file , and just have a few 512-byte blocks of zeros, simply by doing something like 'dd if=bad.file of=bad.file bs=512 conv=noerror' or careful applications of 'skip=N'. If it's compressed, you usually can't recover the rest of a compression group if a previous block is lost. (And for those who talk about backups - yes, taking backups is good. However, it's the rare laptop or desktop machine that can afford the luxury of RAID disks, and backups usually happen once a night, if that often. This means that if you've been working hard on something important all day, and the disk blows chunks at 4:30PM, you *will* be suddenly very concerned over exactly how much you can recover off the failing drive.... And yes, I'd *love* to have all my users connected to nice SAN systems that do snapshotting and remote replication to DR sites and all that - but have you ever *priced* a petabyte of SAN storage, the NAS gateways to serve it to users, and upgrading several tens of thousands of network ports to Gig-E? Hint - US$1M would get us through a pilot, and probably $5M and up to *start* deployment. Anybody wanna buy us an EMC DMX-3? :) http://www.emc.com/products/systems/symmetrix/DMX_series/DMX3.jsp
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