On 6 Nov 2012 12:48 +0000, from h...@carfax.org.uk (Hugo Mills): > There are also some caveats: while the FS should always be > consistent, the latest transaction write may not have been completed, > so you could potentially lose up to 30 seconds of writes to the FS > from immediately before the crash.
I'd rather lose the most recent 30 seconds of writes but have a consistent file system with as-consistent-as-can-be-expected data, than end up with a corrupted file system. On that note; can this value be tuned currently, is it hardcoded, or is it stored in metadata somewhere but the tooling to tune it is not yet available? > If the FS does corrupt over a power failure, and the hardware can > be demonstrated to be good, then we have a bug that needs to be > tracked down. (There have been a number of these over the development > of the FS so far, but they do get fixed). Is there a simple way to tell ahead of time whether the hardware meets the assumptions made by the file system with regards to write barriers etc.? > I guess the question for you is: are you after the _expected_ > behaviour of the FS (should always be consistent on good hardware, but > you may lose up to 30 seconds of writes), or are you after mitigation > strategies in the face of FS bugs (keep off-site backups and be > prepared to use them)? I already have full, daily on-site backups on an external drive that is logically unmounted except for when backups are running, as well as partial off-site backups to cloud storage - and of course, taking advantage of btrfs's snapshotting support there is no real reason why I couldn't increase the backup frequency while retaining data consistency. Losing half a minute of writes is fairly inconsequential for personal use as long as the file system remains consistent, and in the face of disastrous corruption it is at least possible to do a full restore to bare metal from rescue media and backup without losing too much. Not trivial time-wise (that's currently 1.4 TB over USB 2.0), but possible. -- Michael Kjörling • http://michael.kjorling.se • mich...@kjorling.se “People who think they know everything really annoy those of us who know we don’t.” (Bjarne Stroustrup) -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
