Sharing a Logging Device Among File Systems

This section explains how to configure trans metadevices to share logging devices.

Preliminary Information for Sharing a Logging Device

• Once you set up a trans metadevice, you can share the logging device among file systems.

• When sharing a logging device, it is a good idea to make the logging device a mirror.

• Consider sharing a logging device among file systems if your system does not have many available slices, or if the file systems sharing the logging device are read-mostly.

When one master device of a shared logging device goes into an errored state, the logging device is unable to roll its changes forward. This causes all master devices sharing the logging device to go into the hard error state.

How to Share a Logging Device Among File Systems (DiskSuite Tool)

This procedure assumes you have already set up a trans metadevice with a logging device for another file system.

1. Make sure you have met the prerequisites ("Prerequisites for Changing DiskSuite Objects") and have read the preliminary information ("Preliminary Information for Sharing a Logging Device").

2. Identify the slice or metadevice that contains the file system. You'll need this when creating the master device.

   If necessary, click Slices to display the Slice Browser for identifying the slice used by the file system.

3. Click the trans metadevice template.

   An unassigned and uncommitted Trans Metadevice object appears on the canvas. The metadevice name is automatically assigned.

4. [Optional] To change the default metadevice name, display the object's pop-up menu and select Info. Type the new metadevice name in the Device Name field and click Attach. Then click Close.

5. Double-click the existing Trans Metadevice object in the Objects list.

   The objec is displayed on the canvas. The new trans metadevice will share logs with this one.

6. Note the logging device name used by this trans metadevice.

7. Drag the slice from the Slice Browser, or the metadevice from the Objects List, containing the file system to be logged into the master rectangle of the new trans metadevice. A warning dialog box appears. Click Continue.

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   Note -

   If an entry exists in the /etc/vfstab file for the file system, and the file system is currently mounted, DiskSuite Tool automatically updates it to use the trans metadevice's name.

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8. Display the Information window for the new trans metadevice and type the slice or metadevice name noted in the existing trans metadevice (Step 6) into the Log text field.

9. Click Attach. You may see an evaluation warning dialog box. If so, click Accept. Then click Close on the Information window.

10. Click the top rectangle of the Trans Metadevice object then click Commit.

    Click Really Commit on the warning dialog box that appears. This creates the new trans metadevice, sharing the logging device of the existing trans metadevice.

11. To verify that the trans metadevice was committed, display the Configuration Log.

12. Logging becomes effective for the file system when you reboot the system.

    Upon subsequent reboots, instead of checking the file systems, fsck(1M) displays message such as this for each logged file system:

    /dev/md/rdsk/trans: is logging.

How to Share a Logging Device Among File Systems (Command Line)

This procedure assumes you have already set up a trans metadevice with a log for another file system.

After checking the prerequisites ("Prerequisites for Changing DiskSuite Objects"), and the preliminary information ("Preliminary Information for Sharing a Logging Device"), use the metainit(1M) to share a log. Refer to the metainit(1M) man page for more information.

Example -- Sharing a Logging Device

# umount /xyzfs
# metainit d64 -t c0t2d0s4 d10
d64: Trans is setup
(Edit the /etc/vfstab file so that the entry for /xyzfs references the trans metadevice d64)
# mount /xyzfs
# metastat
...
d10: Logging device for d63 d64
...

This example shares a logging device (d10) defined as the log for a previous trans metadevice, with a new trans metadevice (d64). The file system to be set up as the master device is /xyzfs and is using slice /dev/dsk/c0t2d0s4. metainit -t specifies the configuration is a trans metadevice. The /etc/vfstab file must be edited to change (or enter for the first time) the entry for the file system to reference the trans metadevice. For example, the following line:

/dev/dsk/c0t2d0s4 /dev/rdsk/c0t2d0s4 /xyzfs ufs 2 yes -

should be changed to:

/dev/md/dsk/d64 /dev/md/rdsk/d64 /xyzfs ufs 2 yes -

The metastat command verifies that the log is being shared. Logging becomes effective for the file system when the system is rebooted.

Upon subsequent reboots, instead of checking the file system, fsck(1M) displays these messages for the two file systems:

/dev/md/rdsk/d63: is logging.
/dev/md/rdsk/d64: is logging.