On Feb 23, 2007 16:03 -0800, H. Peter Anvin wrote: > Ric Wheeler wrote: > > (1) read-ahead often means that we will retry every bad sector at > >least twice from the file system level. The first time, the fs read > >ahead request triggers a speculative read that includes the bad sector > >(triggering the error handling mechanisms) right before the real > >application triggers a read does the same thing. Not sure what the > >answer is here since read-ahead is obviously a huge win in the normal case. > > Probably the only sane thing to do is to remember the bad sectors and > avoid attempting reading them; that would mean marking "automatic" > versus "explicitly requested" requests to determine whether or not to > filter them against a list of discovered bad blocks. And clearing this list when the sector is overwritten, as it will almost certainly be relocated at the disk level. For that matter, a huge win would be to have the MD RAID layer rewrite only the bad sector (in hopes of the disk relocating it) instead of failing the whiole disk. Otherwise, a few read errors on different disks in a RAID set can take the whole system offline. Apologies if this is already done in recent kernels... Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
