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Thoughts on the ext4 panicThoughts on the ext4 panicPosted Oct 29, 2012 17:29 UTC (Mon) by cesarb (subscriber, #6266)Parent article: Thoughts on the ext4 panic
> One should never underestimate the value of good backups, but, with ext4, the chances of having to actually use those backups remain quite small.
"One should never underestimate the value of good backups, but, with ext4, the chances of having to actually use those backups _because of ext4_ remain quite small."
Fixed. As far as I know, ext4 does nothing to reduce the need for backups (unlike some other filesystems with things like built-in mirroring to separate disks or even separate machines).
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Thoughts on the ext4 panic Posted Nov 8, 2012 6:00 UTC (Thu) by kevinm (guest, #69913) [Link]
Mirroring, whether to separate disks or separate machines, also does nothing to reduce the need for backups.
In the case of application- or user- level corruption, mirroring will simply replicate the error very efficiently.
Thoughts on the ext4 panic Posted Nov 8, 2012 7:49 UTC (Thu) by dlang (✭ supporter ✭, #313) [Link]
to err is human, to really foul things up requires a computer
and to _really_ trash things requires automation :-)
automated replication (including mirroring) is a wonderful way to propagate corruption (as someone who has automated the trashing of several hundred systems with a single command, I can really attest to this one)
Thoughts on the ext4 panic Posted Nov 8, 2012 15:34 UTC (Thu) by nix (subscriber, #2304) [Link]
Quite. I did, after all, spot this problem on a hardware RAID-5 array. The RAIDness of the array didn't help: the corruption was faithfully written out. It had neither the evil nor corrupted bits set, after all.
Thoughts on the ext4 panic Posted Nov 11, 2012 2:16 UTC (Sun) by steffen780 (guest, #68142) [Link]
Sorry, but that claim is just wrong. Mirroring and replication do REDUCE the need for backups. They do, however, not ELIMINATE it. They protect against many forms of hardware failure, including what I would assume is the most common cause of hw-caused data loss: disk failures. Hence they reduce the need for backups. Of course they do not get rid of user-/app-level failures. They're not supposed to (and by definition cannot), and hence they do not eliminate the need for backups... but they do definitely reduce it.
Thoughts on the ext4 panic Posted Nov 12, 2012 3:58 UTC (Mon) by kevinm (guest, #69913) [Link]
The need for backups is binary - you either need backups, or you don't need backups.
Thoughts on the ext4 panic Posted Nov 12, 2012 5:10 UTC (Mon) by neilbrown (subscriber, #359) [Link]
The backups you need can take any of a range of values from none to offsite copies that let you reconstruct the state of anything at any moment.
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