By default, when multihost is enabled for a pool, the pool is
suspended if (zfs_multihost_fail_intervals*zfs_multihost_interval) ms
pass without a successful MMP write. This is the recommended
configuration.
The default value for zfs_multihost_fail_intervals has been 5, and the
default value for zfs_multihost_interval has been 1000, so pool
suspension occurred at 5 seconds.
There have been multiple cases where a single misbehaving device in a
pool triggered a SCSI reset, and all I/O paused for 5-6 seconds. This
in turn caused MMP to suspend the pool.
In the cases observed, the rest of the devices were healthy and the
pool was otherwise correctly performing I/O. The reset was handled
correctly by ZFS, and by suspending the pool MMP made replacing the
device more difficult as well as forcing the host to be rebooted.
Increase the default value of zfs_multihost_fail_intervals to 10, so
that MMP tolerates up to 10 seconds of failed MMP writes before
suspending the pool.
Increase the default value of zfs_multihost_import_intervals to 20, to
maintain the 2:1 safety factor. This results in a force import taking
approximately 20 seconds when MMP is enabled, with default values.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Andreas Dilger <andreas.dilger@whamcloud.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes#7709Closes#8495
Instead of choosing a leaf vdev quasi-randomly, by starting at the root
vdev and randomly choosing children, rotate over leaves to issue MMP
writes. This fixes an issue in a pool whose top-level vdevs have
different numbers of leaves.
The issue is that the frequency at which individual leaves are chosen
for MMP writes is based not on the total number of leaves but based on
how many siblings the leaves have.
For example, in a pool like this:
root-vdev
+------+---------------+
vdev1 vdev2
| |
| +------+-----+-----+----+
disk1 disk2 disk3 disk4 disk5 disk6
vdev1 and vdev2 will each be chosen 50% of the time. Every time vdev1
is chosen, disk1 will be chosen. However, every time vdev2 is chosen,
disk2 is chosen 20% of the time. As a result, disk1 will be sent 5x as
many MMP writes as disk2.
This may create wear issues in the case of SSDs. It also reduces the
effectiveness of MMP as it depends on the writes being evenly
distributed for the case where some devices fail or are partitioned.
The new code maintains a list of leaf vdevs in the pool. MMP records
the last leaf used for an MMP write in mmp->mmp_last_leaf. To choose
the next leaf, MMP starts at mmp->mmp_last_leaf and traverses the list,
continuing from the head if the tail is reached. It stops when a
suitable leaf is found or all leaves have been examined.
Added a test to verify MMP write distribution is even.
Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Kash Pande <kash@tripleback.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes#7953
Once per pass through the MMP thread's loop, the vdev tree is walked to
find a suitable leaf to write the next MMP block to. If no such leaf is
found, the thread sleeps for a while and resumes at the top of the loop.
Add an entry to multihost_history when no leaf can be found, and record
the reason in the error column. The error code for such entries is a
bitfield, displayed in hex:
0x1 At least one vdev (interior or leaf) was not writeable.
0x2 At least one writeable leaf vdev was found, but it had a pending
MMP write.
timestamp = the time in seconds since the epoch when no leaf could be
found originally.
duration = the time (in ns) during which no MMP block was written for
this reason. This does not include the preceeding inter-write period
nor the following inter-write period.
vdev_guid = the number of sequential cycles of the MMP thread looop when
this occurred.
Sample output, truncated to fit:
For records of skipped MMP writes the right-most column, vdev_path, is
reported as "-".
id txg timestamp error duration mmp_delay vdev_guid ...
936 11 1520036441 0 146264 891422313 1740883117838 ...
937 11 1520036441 0 163956 888356657 7320395061548 ...
938 11 1520036442 0 130690 885314969 7320395061548 ...
939 11 1520036442 0 2001068577 882296582 1740883117838 ...
940 11 1520036443 0 161806 882296582 7320395061548 ...
941 11 1520036443 0x2 0 998020546 1 ...
942 11 1520036444 0 136585 998020546 7320395061548 ...
943 11 1520036444 0x2 0 998020257 1 ...
944 11 1520036445 5 2002662964 994160219 1740883117838 ...
945 11 1520036445 0x2 998073118 994160219 3 ...
946 11 1520036447 0 247136 994160219 7320395061548 ...
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes#7212
Add a callback to wake all running mmp threads when
zfs_multihost_interval is changed.
This is necessary when the interval is changed from a very large value
to a significantly lower one, while pools are imported that have the
multihost property enabled.
Without this commit, the mmp thread does not wake up and detect the new
interval until after it has waited the old multihost interval time. A
user monitoring mmp writes via the provided kstat would be led to
believe that the changed setting did not work.
Added a test in the ZTS under mmp to verify the new functionality is
working.
Added a test to ztest which starts and stops mmp threads, and calls into
the code to signal sleeping mmp threads, to test for deadlocks or
similar locking issues.
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes#6387
Add multihost=on|off pool property to control MMP. When enabled
a new thread writes uberblocks to the last slot in each label, at a
set frequency, to indicate to other hosts the pool is actively imported.
These uberblocks are the last synced uberblock with an updated
timestamp. Property defaults to off.
During tryimport, find the "best" uberblock (newest txg and timestamp)
repeatedly, checking for change in the found uberblock. Include the
results of the activity test in the config returned by tryimport.
These results are reported to user in "zpool import".
Allow the user to control the period between MMP writes, and the
duration of the activity test on import, via a new module parameter
zfs_multihost_interval. The period is specified in milliseconds. The
activity test duration is calculated from this value, and from the
mmp_delay in the "best" uberblock found initially.
Add a kstat interface to export statistics about Multiple Modifier
Protection (MMP) updates. Include the last synced txg number, the
timestamp, the delay since the last MMP update, the VDEV GUID, the VDEV
label that received the last MMP update, and the VDEV path. Abbreviated
output below.
$ cat /proc/spl/kstat/zfs/mypool/multihost
31 0 0x01 10 880 105092382393521 105144180101111
txg timestamp mmp_delay vdev_guid vdev_label vdev_path
20468 261337 250274925 68396651780 3 /dev/sda
20468 261339 252023374 6267402363293 1 /dev/sdc
20468 261340 252000858 6698080955233 1 /dev/sdx
20468 261341 251980635 783892869810 2 /dev/sdy
20468 261342 253385953 8923255792467 3 /dev/sdd
20468 261344 253336622 042125143176 0 /dev/sdab
20468 261345 253310522 1200778101278 2 /dev/sde
20468 261346 253286429 0950576198362 2 /dev/sdt
20468 261347 253261545 96209817917 3 /dev/sds
20468 261349 253238188 8555725937673 3 /dev/sdb
Add a new tunable zfs_multihost_history to specify the number of MMP
updates to store history for. By default it is set to zero meaning that
no MMP statistics are stored.
When using ztest to generate activity, for automated tests of the MMP
function, some test functions interfere with the test. For example, the
pool is exported to run zdb and then imported again. Add a new ztest
function, "-M", to alter ztest behavior to prevent this.
Add new tests to verify the new functionality. Tests provided by
Giuseppe Di Natale.
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Ned Bass <bass6@llnl.gov>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes#745Closes#6279
Olaf Faaland