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Commit 9fd7ac7d03 did not handle mirrors
that contained mirrored logs. This is because the status line of the
mirror does not give an indication of the health of the mirrored log,
as you can see here:
[root@bp-01 lvm2]# dmsetup status vg-lv vg-lv_mlog
vg-lv: 0 409600 mirror 2 253:6 253:7 400/400 1 AA 3 disk 253:5 A
vg-lv_mlog: 0 8192 mirror 2 253:3 253:4 7/8 1 AD 1 core
Thus, the possibility for LVM commands to hang still persists when mirror
have mirrored logs. I discovered this while performing some testing that
does polling with 'pvs' while doing I/O and killing devices. The 'pvs'
managed to get between the mirrored log device failure and the attempt
by dmeventd to repair it. The result was a very nasty block in LVM
commands that is very difficult to remove - even for someone who knows
what is going on. Thus, it is absolutely essential that the log of a
mirror be recursively checked for mirror devices which may be failed
as well.
Despite what the code comment says in the aforementioned commit...
+ * _mirrored_transient_status(). FIXME: It is unable to handle mirrors
+ * with mirrored logs because it does not have a way to get the status of
+ * the mirror that forms the log, which could be blocked.
... it is possible to get the status of the log because the log device
major/minor is given to us by the status output of the top-level mirror.
We can use that to query the log device for any DM status and see if it
is a mirror that needs to be bypassed. This patch does just that and is
now able to avoid reading from mirrors that have failed devices in a
mirrored log.
Addresses: rhbz855398 (Allow VGs to be built on cluster mirrors),
and other issues.
The LVM code attempts to avoid reading labels from devices that are
suspended to try to avoid situations that may cause the commands to
block indefinitely. When scanning devices, 'ignore_suspended_devices'
can be set so the code (lib/activate/dev_manager.c:device_is_usable())
checks any DM devices it finds and avoids them if they are suspended.
The mirror target has an additional mechanism that can cause I/O to
be blocked. If a device in a mirror fails, all I/O will be blocked
by the kernel until a new table (a linear target or a mirror with
replacement devices) is loaded. The mirror indicates that this condition
has happened by marking a 'D' for the faulty device in its status
output. This condition must also be checked by 'device_is_usable()' to
avoid the possibility of blocking LVM commands indefinitely due to an
attempt to read the blocked mirror for labels.
Until now, mirrors were avoided if the 'ignore_suspended_devices'
condition was set. This check seemed to suggest, "if we are concerned
about suspended devices, then let's ignore mirrors altogether just
in case". This is insufficient and doesn't solve any problems. All
devices that are suspended are already avoided if
'ignore_suspended_devices' is set; and if a mirror is blocking because
of an error condition, it will block the LVM command regardless of the
setting of that variable.
Rather than avoiding mirrors whenever 'ignore_suspended_devices' is
set, this patch causes mirrors to be avoided whenever they are blocking
due to an error. (As mentioned above, the case where a DM device is
suspended is already covered.) This solves a number of issues that weren't
handled before. For example, pvcreate (or any command that does a
pv_read or vg_read, which eventually call device_is_usable()) will be
protected from blocked mirrors regardless of how
'ignore_suspended_devices' is set. Additionally, a mirror that is
neither suspended nor blocking is /allowed/ to be read regardless
of how 'ignore_suspended_devices' is set. (The latter point being the
source of the fix for rhbz855398.)
The heading 'Copy%' is specific to PVMOVE volumes, but can be generalized
to apply to LVM mirrors also. It is a bit awkward to use 'Copy%' for
RAID 4/5/6, however - 'Sync%' would be more appropriate. This is why
RAID 4/5/6 have not displayed their sync status by any means available to
'lvs' yet.
Example (old):
[root@hayes-02 lvm2]# lvs vg
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sy Convert
lv vg -wi-a---- 1.00g
raid1 vg rwi-a-r-- 1.00g 100.00
raid4 vg rwi-a-r-- 1.01g
raid5 vg rwi-a-r-- 1.01g
raid6 vg rwi-a-r-- 1.01g
This patch changes the heading to 'Cpy%Sync' and allows RAID 4/5/6 to print
their sync percent in this field.
Example (new):
[root@hayes-02 lvm2]# lvs vg
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert
lv vg -wi-a---- 1.00g
raid1 vg rwi-a-r-- 1.00g 100.00
raid4 vg rwi-a-r-- 1.01g 100.00
raid5 vg rwi-a-r-- 1.01g 100.00
raid6 vg rwi-a-r-- 1.01g 100.00
The 'copy_percent' function takes the 'extents_copied' field from each
segment in an LV to create the numerator for the ratio that is to
become the copy_percent. (Otherwise known as the 'sync' percent for
non-pvmove uses, like mirror LVs and RAID LVs.) This function safely
works on RAID - not just mirrors - so it is better to have it in
lv_manip.c rather than mirror.c.
There's a lot of different functions that do a lot of different things
in lv_manip.c, so I placed the function near a function in lv_manip.c
that it was close to in metadata-exported.h. Different placement in the
file or a different name for the function may be useful.
Use log_warn to print non-fatal warning messages.
Use of log_error would confuse checker for testing
whether proper error has been reported for some real error.
A message is printed when the region_size of a RAID LV is adjusted
to allow for large (> ~1TB) LVs. The message wasn't very clear.
Hopefully, this is better.
When valgrind usage is desired by user (--enable-valgrind-pool)
skip playing/closing/reopenning with descriptors - it makes
valgridng useless.
Make sleep delay for clvmd start longer.
Use configure --enable-python_bindings to generate them.
Note that the Makefiles do not yet control the owner or permissions of
the two new files on installation.
It would be possible to activate a RAID LV exclusively in a cluster
volume group, but for now we do not allow RAID LVs to exist in a
clustered volume group at all. This has two components:
1) Do not allow RAID LVs to be created in a clustered VG
2) Do not allow changing a VG from single-machine to clustered
if there are RAID LVs present.
MD's bitmaps can handle 2^21 regions at most. The RAID code has always
used a region_size of 1024 sectors. That means the size of a RAID LV was
limited to 1TiB. (The user can adjust the region_size when creating a
RAID LV, which can affect the maximum size.) Thus, creating, extending or
converting to a RAID LV greater than 1TiB would result in a failure to
load the new device-mapper table.
Again, the size of the RAID LV is not limited by how much space is allocated
for the metadata area, but by the limitations of the MD bitmap. Therefore,
we must adjust the 'region_size' to ensure that the number of regions does
not exceed the limit. I've added code to do this when extending a RAID LV
(which covers 'create' and 'extend' operations) and when up-converting -
specifically from linear to RAID1.
We were using daemon_send_simple until now, but it is no longer adequate, since
we need to manipulate requests in a generic way (adding a validity token to each
request), and the tree-based request interface is much more suitable for this.
