ZFS Snapshots Not able to be accessed under .zfs/snapshot/name

Thu Aug 15 15:00:49 UTC 2013

On 08/14/2013 9:43 pm, Shane Ambler wrote:
> On 14/08/2013 22:57, dweimer wrote:
>> I have a few systems running on ZFS with a backup script that creates
>> snapshots, then  backs up the .zfs/snapshot/name directory to make 
>> sure
>> open files are not missed.  This has been working great but all of the
>> sudden one of my systems has stopped working.  It takes the snapshots
>> fine, zfs list -t spnapshot shows the snapshots, but if you do an ls
>> command, on the .zfs/snapshot/ directory it returns not a directory.
>> 
>> part of the zfs list output:
>> 
>> NAME                        USED  AVAIL  REFER  MOUNTPOINT
>> zroot                      4.48G  29.7G    31K  none
>> zroot/ROOT                 2.92G  29.7G    31K  none
>> zroot/ROOT/91p5-20130812   2.92G  29.7G  2.92G  legacy
>> zroot/home                  144K  29.7G   122K  /home
>> 
>> part of the zfs list -t snapshot output:
>> 
>> NAME                                            USED  AVAIL  REFER
>> MOUNTPOINT
>> zroot/ROOT/91p5-20130812 at 91p5-20130812--bsnap   340K      -  2.92G  -
>> zroot/home at home--bsnap                           22K      -   122K  -
>> 
>> ls /.zfs/snapshot/91p5-20130812--bsnap/
>> Does work at the right now, since the last reboot, but wasn't always
>> working, this is my boot environment.
>> 
>> if I do ls /home/.zfs/snapshot/, result is:
>> ls: /home/.zfs/snapshot/: Not a directory
>> 
>> if I do ls /home/.zfs, result is:
>> ls: snapshot: Bad file descriptor
>> shares
>> 
>> I have tried zpool scrub zroot, no errors were found, if I reboot the
>> system I can get one good backup, then I start having problems.  
>> Anyone
>> else ever ran into this, any suggestions as to a fix?
>> 
>> System is running FreeBSD 9.1-RELEASE-p5 #1 r253764: Mon Jul 29 
>> 15:07:35
>> CDT 2013, zpool is running version 28, zfs is running version 5
>> 
> 
> 
> I can say I've had this problem. Not certain what fixed it. I do
> remember I decided to stop snapshoting if I couldn't access them and
> deleted existing snapshots. I later restarted the machine before I
> went back for another look and they were working.
> 
> So my guess is a restart without existing snapshots may be the key.
> 
> Now if only we could find out what started the issue so we can stop it
> happening again.

I had actually rebooted it last night, prior to seeing this message, I 
do know it didn't have any snapshots this time.  As I am booting from 
ZFS using boot environments I may have had an older boot environment 
still on the system the last time it was rebooted.  Backups ran great 
last night after the reboot, and I was able to kick off my pre-backup 
job and access all the snapshots today.  Hopefully it doesn't come back, 
but if it does I will see if I can find anything else wrong.

FYI,
It didn't shutdown cleanly, so if this helps anyone find the issue, this 
is from my system logs:
Aug 14 22:08:04 cblproxy1 kernel:
Aug 14 22:08:04 cblproxy1 kernel: Fatal trap 12: page fault while in 
kernel mode
Aug 14 22:08:04 cblproxy1 kernel: cpuid = 0; apic id = 00
Aug 14 22:08:04 cblproxy1 kernel: fault virtual address = 0xa8
Aug 14 22:08:04 cblproxy1 kernel: fault code            = supervisor 
write data, page not present
Aug 14 22:08:04 cblproxy1 kernel: instruction pointer   = 
0x20:0xffffffff808b0562
Aug 14 22:08:04 cblproxy1 kernel: stack pointer         = 
0x28:0xffffff80002238f0
Aug 14 22:08:04 cblproxy1 kernel: frame pointer         = 
0x28:0xffffff8000223910
Aug 14 22:08:04 cblproxy1 kernel: code segment          = base 0x0, 
limit 0xfffff, type 0x1b
Aug 14 22:08:04 cblproxy1 kernel: = DPL 0, pres 1, long 1, def32 0, gran 
1
Aug 14 22:08:04 cblproxy1 kernel: processor eflags      = interrupt 
enabled, resume, IOPL = 0
Aug 14 22:08:04 cblproxy1 kernel: current process               = 1 
(init)
Aug 14 22:08:04 cblproxy1 kernel: trap number           = 12
Aug 14 22:08:04 cblproxy1 kernel: panic: page fault
Aug 14 22:08:04 cblproxy1 kernel: cpuid = 0
Aug 14 22:08:04 cblproxy1 kernel: KDB: stack backtrace:
Aug 14 22:08:04 cblproxy1 kernel: #0 0xffffffff808ddaf0 at 
kdb_backtrace+0x60
Aug 14 22:08:04 cblproxy1 kernel: #1 0xffffffff808a951d at panic+0x1fd
Aug 14 22:08:04 cblproxy1 kernel: #2 0xffffffff80b81578 at 
trap_fatal+0x388
Aug 14 22:08:04 cblproxy1 kernel: #3 0xffffffff80b81836 at 
trap_pfault+0x2a6
Aug 14 22:08:04 cblproxy1 kernel: #4 0xffffffff80b80ea1 at trap+0x2a1
Aug 14 22:08:04 cblproxy1 kernel: #5 0xffffffff80b6c7b3 at calltrap+0x8
Aug 14 22:08:04 cblproxy1 kernel: #6 0xffffffff815276da at 
zfsctl_umount_snapshots+0x8a
Aug 14 22:08:04 cblproxy1 kernel: #7 0xffffffff81536766 at 
zfs_umount+0x76
Aug 14 22:08:04 cblproxy1 kernel: #8 0xffffffff809340bc at 
dounmount+0x3cc
Aug 14 22:08:04 cblproxy1 kernel: #9 0xffffffff8093c101 at 
vfs_unmountall+0x71
Aug 14 22:08:04 cblproxy1 kernel: #10 0xffffffff808a8eae at 
kern_reboot+0x4ee
Aug 14 22:08:04 cblproxy1 kernel: #11 0xffffffff808a89c0 at 
kern_reboot+0
Aug 14 22:08:04 cblproxy1 kernel: #12 0xffffffff80b81dab at 
amd64_syscall+0x29b
Aug 14 22:08:04 cblproxy1 kernel: #13 0xffffffff80b6ca9b at 
Xfast_syscall+0xfb

-- 
Thanks,
    Dean E. Weimer
    http://www.dweimer.net/