Hmm, true. The idea doesn't work so well if you have a lot of writes, so there needs to be some thought as to how you handle that.
Just thinking aloud, could the missing writes be written to the log file on the rest of the pool? Or temporarily stored somewhere else in the pool? Would it be an option to allow up to a certain amount of writes to be cached in this way while waiting for FMA, and only suspend writes once that cache is full? With a large SSD slog device would it be possible to just stream all writes to the log? As a further enhancement, might it be possible to commit writes to the working drives, and just leave the writes for the bad drive(s) in the slog (potentially saving a lot of space)? For pools without log devices, I suspect that you would probably need the administrator to specify the behavior as I can see several options depending on the raid level and that pools priorities for data availability / integrity: Drive fault write cache settings: default - pool waits for device, no writes occur until device or spare comes online slog - writes are cached to slog device until full, then pool reverts to default behavior (could this be the default with slog devices present?) pool - writes are cached to the pool itself, up to a set maximum, and are written to the device or spare as soon as possible. This assumes a single parity pool with the other devices available. If the upper limit is reached, or another devices goes faulty, pool reverts to default behaviour. Storing directly to the rest of the pool would probably want to be off by default on single parity pools, but I would imagine that it could be on by default on dual parity pools. Would that be enough to allow writes to continue in most circumstances while the pool waits for FMA? Ross On Tue, Nov 25, 2008 at 10:55 AM, <[EMAIL PROTECTED]> wrote: > > >>My idea is simply to allow the pool to continue operation while >>waiting for the drive to fault, even if that's a faulty write. It >>just means that the rest of the operations (reads and writes) can keep >>working for the minute (or three) it takes for FMA and the rest of the >>chain to flag a device as faulty. > > Except when you're writing a lot; 3 minutes can cause a 20GB backlog > for a single disk. > > Casper > > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
