HP StorageWorks Storage Mirroring for Linux User's Guide (T2558-96317, June 2009)

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1.3.2. Configure Block Device Replication setup file—In order to use Storage
Mirroring replication, data that will be replicated on a block device must be
accessed through a loop device which is specially attached using the Storage
Mirroring loop driver (DTLOOP). DTLOOP allows the loop device to serve as a
monitoring point for operations performed on the block device so that data
changes can be captured. Existing block devices may be available for
replication, but the data on those block devices can only be replicated if they are
accessed through the DTLOOP loop device. It is important that operations on the
block device be made through the loop device only, or the operations will not be
replicated. Failure to do so will result in corrupted data on the target system.
1.3.2.1. Add an entry to /etc/DT/dtloop_devices—Enter the path to the
block device that is to be replicated and press Enter. Then, enter the
path to the loop device to use (/dev/loop#), if the same one should
always be attached. DTLOOP can also use the first one available, but
that may mean it attaches to a different one on subsequent
reboots/restarts, which may not be desirable. After pressing Enter, you
will be asked if you want to attach at an offset into the block device and
if you want to use an encrypted loop device. In general, these options
can be left blank. See the documentation for losetup for more
information on using encryption. You can either stop and restart the
Storage Mirroring daemon so that new entries in
/etc/DT/dtloop_devices will take effect or you can mount the entries
immediat
ely usin
g menu option 1.3.2.3.
1.3.2.2. Remove an entry from /etc/DT/dtloop_devices—Enter the path of
the block device that needs to be removed.
1.3.2.3. Attach all entries in /etc/DT/dtloop_devices to a loop device—
This option will cause the entries of the list to be attached to loop
devices with DTFS immediately, rather than when the daemon is
started. This allows you to review the effects of the changes and
troubleshoot any issues.
1.3.2.4. Detach loop devices from all entries in
/etc/DT/dtloop_devices—This option
will detach the DTLOOP loop
device from the b
lock devices on the system, if any. This allows you to
make changes to the DTLOOP loop devices without unloading the
daemon.
1.3.2.5. List block devices on this system—This option will provide a list of
block devices to which DTLOOP can be attached. Use this list as a guide
for menu option 1.3.2.1.
1.3.3. Manual Replication Configuration menu—This option will take you to the
menu where the file system and block device replication configuration can be
changed but not persisted between reboots/restarts.
1.3.3.1. Manually mount DTFS on a file system—Type the path of the
highest subdirectory for which replication should be captured. This can
be the path to a mount point or a subdirectory of a volume.
1.3.3.2. Manually unmount a DTFS file system—Type the path of the entry
that needs to be removed from replication.
NOTE: You will be prompted whether you want to replicate access
times. The access-time file property changes during a mirror
and causes replication operations to be generated during a
mirror and every time a file is read from or written to. This
may have a negative effect on performance. If you do not
replicate access times on both the source and target when
the volume is initially mounted, you may increase the
performance, especially during mirroring. (Access times
from files closes are always replicated regardless of this
configuration.)