On Tue, 2004-06-29 at 15:56, Dieter Stueken wrote: > Mike Tran wrote: > > (Please note that I don't mean to advertise EVMS here :) just want to > > mention that the functionality is available) > > > > EVMS, (http://evms.sourceforge.net) provides a solution to this "bad > > sectors" issue by having Bad Block Relocation (BBR) layer on the I/O > > stack. > > Before proposing any solutions, i think it is very important to > distinguish carefully between different kinds of errors: > > a) read errors: some alert bell should ring (syslog/mail..) > but the system should not careless disable any disk to avoid > making the problem even worse. > > b) write errors: if some blocks are written partly, but can not > be written to all disks, it may help, to write the data > (may be temporary) somewhere else. > > when we got a read error, due to an unreadable sector, we may > first try to rewrite it. In most cases, bad sector replacement > of the HD-firmware takes action and the problem is solved so far. > For raid1 mirroring, I think the code for "rewrite" does not look too bad. For raid5/raid5, it's going be harder. I'm not saying that it's not doable :) In fact, there is a cnt_corrected_read field in the MD ver 1 superblock. So, I hope this feature is coming soon. > Only after this failed, we should turn over to plan b) > > case b) may also help, if some disk gets temporary unavailable > (i.E. cabling problem). After manual intervention, that brings > the disk back on line again, the redirected data may even be > copied back. > Plan b) needs that "somewhere else." This can also be achieved with the MD ver 1 superblock. Where we can reserve some sectors by correcly setting the usable data_offset and data_size. Now, we need user-space tool to create MD arrays with ver 1 superblock. In addition, of course, we will also need to enhance MD kernel code. Cheers, Mike T. - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
