fsck

And finally, it happend.

On Monday, one of our server, running FreeBSD, panic’ed with “ffs_clusteralloc: map mismatch”. This message is quite uncommon and should only happen when there is some “event” with the memory or hard disk.

I have suggested our administrator to reboot and do “fsck” on the volume, since it has very small block size and can not be checked background (I have made a change to warn about this to FreeBSD, and was MFC’ed to 5-STABLE so you will get the feature in 5.4-RELEASE). Unfortunatelly, the check is so slow and we start to suspect whether there is some hardware problem.

1. We should not caclucate the superblock summary, since it can at most lag 30 seconds’ change, and doing the caclucate is painful delay. What we should do is to transfer the responsibility to background fsck
2. newfs(8) should warn about the snapshot is actually unable to create, in case fssize is greater than maxfilesize.

The patch for 1) is available at http://people.freebsd.org/~delphij/ffs/patch-sbsummary. I will work on 2) shortly, as it’s quite simpler than 1).