Since I have been experiencing some mysterious file system corruption on a fs that was fsck-clean before being mounted, I would like to periodically fsck that fs while mounted. The problem is that fs is 6T large.
If I use an internal snapshot (fsck_ffs -X), the server stalls for about an hour, then panics (wapbl_deregister_allocation: out of resources) and, upon reboot, needs longer for replaying the journal than an fsck would take. If I use an external snapshot (fsck_ffs -x /somewhere/else), the snapshot only takes a few seconds, but fsck_ffs complains about unreferenced files, missing blocks in the free list and bad summary information. I have tested both -x and -X on a smaller fs, and -X runs fine while -x complains. So why do internal and external snapshots behave so differently? Are they just two completely diffrent aproaches to the same problem or what's the reason for using what seems to be a totally different strategy when the backup file is inside the fs itself? Is there any documentation on the subject?
