(moving my thread from -fs to -stable)
Before touching anything, here's a description of the symptoms I
see... Rather busy system, with quite a bit of filesystem activity
occurring while the snapshot is being made. Quad CPU amd64 box with
16GB of ram, 6x10Krpm RAID array. Should be reasonably fast.
Filesystem 1K-blocks Used Avail Capacity iused ifree
%iused Mounted on
/dev/da0s1a 739339824 74357926 605834714 11% 1718540
93855474 2% /
1.7 million inodes, 71G used of a 705G volume.
Here's a timeline of what I see when starting to make a new snapshot.
I've got a few windows running, showing "top", "iostat", etc.
Baseline disk activity before starting anything:
device r/s w/s kr/s kw/s wait svc_t b
da0 24.0 2.0 355.6 32.0 1 10.7 28
0m0s: Snapshot begins, using "mount -u -o snapshot //.snap/weekly.
0 /" Drives immediately jump to 100% busy as expected.
device r/s w/s kr/s kw/s wait svc_t b
da0 153.8 6.0 3378.6 95.9 2 16.9 100
the mount process is spending 100% of its time in "biord".
2m10s: The mount process starts spending more and more time in
"snaplk", alternating with "biord".
device r/s w/s kr/s kw/s wait svc_t b
da0 77.9 67.9 1270.7 3754.2 1 10.7 100
12m15s: The first intermittent slowdowns start affecting other
processes on the system. Occasionally all active processes will get
stuck in "snaplk" or "ufs" for 5-10 seconds before resuming.
device r/s w/s kr/s kw/s wait svc_t b
da0 77.9 31.0 1150.8 1054.9 1 10.4 100
114m47s: Active processes are briefly stuck in "suspfs"
115m22s: Mount is now in "snaprdb", Active processes are now
completely stuck in "snaplk". Still responsive to SIGINFO, top is
still running, etc. Just hangs any time anything needs the filesystem.
device r/s w/s kr/s kw/s wait svc_t b
da0 238.8 0.0 3820.1 0.0 1 4.1 99
143m19s: Mount now in wdrain.
143m34s: Finished.
snapshot logging shows "/: suspended 13.308 sec, redo 153 of 4058"
Most processes were hung for 28 minutes.
Is this what others are seeing? It sounds like some of the complaints
are it getting stuck in the "wdrain" state, not what I'm showing here.
Another mildly annoying note: Any process that touches ".snap" while a
snapshot is being generated gets stuck in "ufs" until it finishes. I
can understand wanting to keep operations in there in sync, but it
would be really nice if "find /" wouldn't get hung when it tries to
decent into .snap, for example.
ts5# cd /.snap
ts5# ls -l
^T
load: 0.17 cmd: ls 3696 [ufs] 0.00u 0.00s 0% 1496k
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