Red Hat ENTERPRISE LINUX 5.5 - S 2010, Руководство пользователя

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ctdb
305
5.4. ctdb
CTDB is a clustered database based on Samba's Trivial Database (TDB). The ctdb package is
a cluster implementation used to store temporary data. If an application is already using TBD for
temporary data storage, it can be very easily converted to be cluster-aware and use CTDB.
• When installing ctdb, the tdb-tools package needs to be installed manually. This dependency issues
will be addressed in a future release. (
BZ#526479
23
)
5.5. device-mapper-multipath
The device-mapper-multipath packages provide tools to manage multipath devices using the device-
mapper multipath kernel module.
• When using
dm-multipath
, if
features "1 queue_if_no_path"
is specified in
/etc/
multipath.conf
then any process that issues I/O will hang until one or more paths are restored.
To avoid this, set
no_path_retry [N]
in
/etc/multipath.conf
(where
[N]
is the
number of times the system should retry a path). When you do, remove the
features "1
queue_if_no_path"
option from
/etc/multipath.conf
as well.
If you need to use
"1 queue_if_no_path"
and experience the issue noted here, use
dmsetup
to edit the policy at runtime for a particular LUN (i.e. for which all the paths are unavailable).
To illustrate: run
dmsetup message [device] 0 "fail_if_no_path"
, where
[device]
is
the multipath device name (e.g.
mpath2
; do not specify the path) for which you want to change the
policy from
"queue_if_no_path"
to
"fail_if_no_path"
.
(BZ#419581)
24
• When a LUN is deleted on a configured storage system, the change is not reflected on the host. In
such cases,
lvm
commands will hang indefinitely when
dm-multipath
is used, as the LUN has
now become
stale
.
To work around this, delete all device and
mpath
link entries in
/etc/lvm/.cache
specific to the
stale LUN.
To find out what these entries are, run the following command:
ls -l /dev/mpath | grep [stale LUN]
For example, if
[stale LUN]
is 3600d0230003414f30000203a7bc41a00, the following results may
appear:
lrwxrwxrwx 1 root root 7 Aug 2 10:33 -/3600d0230003414f30000203a7bc41a00 --> -../dm-4
lrwxrwxrwx 1 root root 7 Aug 2 10:33 -/3600d0230003414f30000203a7bc41a00p1 --> -../dm-5
This means that 3600d0230003414f30000203a7bc41a00 is mapped to two
mpath
links:
dm-4
and
dm-5
.
As such, the following lines should be deleted from
/etc/lvm/.cache
:
/dev/dm-4
/dev/dm-5
/dev/mapper/3600d0230003414f30000203a7bc41a00