We've had several servers end up with read-only JFS volumes shortly after reboot recently. I'm not sure how backlevel we are on jfs & jfsutils, but here's some data I gathered data on 2 of them.

System 1:
Jun  1 20:11:21 rchs73gd kernel: ERROR: (device sd(8,17)): dbAllocAG: unable to allocate blocks
Jun  1 20:11:21 rchs73gd kernel: ERROR: (device sd(8,17)): remounting filesystem as read-only

Red Hat Enterprise Linux ES release 3 (Taroon Update 5)
jfsutils-1.1.7-2
Linux rchs73gd.xxx 2.4.21-47.0.1.ELsmp #1 SMP Fri Oct 13 17:56:20 EDT 2006 i686 i686 i386 GNU/Linux
This one is running a jfs.o that we built based on the "original" RH shipped JFS source + patches from about Jan 2006.

System 2: (standard code from SuSE)
Jun  4 04:11:33 as1lnx2 kernel: ERROR: (device sdb1): XT_GETPAGE: xtree page corrupt
Jun  4 04:11:33 as1lnx2 kernel: ERROR: (device sdb1): XT_GETPAGE: xtree page corrupt

# uname -a
Linux as1lnx2 2.6.5-7.282-pseries64 #1 SMP Tue Aug 29 10:40:40 UTC 2006 ppc64 ppc64 ppc64 GNU/Linux
# cat /etc/SuSE-release
SUSE LINUX Enterprise Server 9 (ppc)
VERSION = 9
PATCHLEVEL = 3

On this one, fsck reported:

**Phase 4 - Report Problems
File system object FF12387 is linked as: /lbmarsh/tsmacl_rst/tsmacl/aclfile
cannot repair the data format error(s) in this file.
cannot repair FF12387.  Will release.

Thanks,
Bill