Creating JFS2 file systems? Not so fast!
AnthonyEnglish 270000RKFN Comments (8) Visits (19011)
Often in SMIT you can use the default settings, but when it comes to creating Enhanced Journalled File Systems – better known as JFS2 – there are three options which you’ll probably want to change from the defaults.
Of course you need to set the MOUNT POINT, but the other three I like to change are:
Here are the entries I change from the default when I create an enhanced Journalled File System using SMIT:
Mount automatically on system restart?
Ever find a new file system has gone missing after a reboot? You might have forgotten to change the automatic mount setting to yes when you created the file system. If you do set it to yes, the "mount" option will be set to true, as you can see from this in /etc/filesystems:
Any file systems with the mount option set to true will attempt to be mounted when you run either:
INLINE JFS2 Log
Setting the Logical Volume for Log attribute to INLINE means the JFS2 log is contained within the logical volume itself. This obviously helps avoid contention with other file systems, which would happen if they were all sharing the same JFS2log.
The oft-quoted Chris Gibson has yet another great article. This one's on JFS2 snapshots. As Chris explains, they allow you to create consistent, integrated snapshots of an online (or offline) JFS2 file system, in other words rapid, point-in-time copies which take up very little disk space. Even if I don't use them, when I create a JFS2 file system these days, from now on the "Allow internal snapshots" gets the tick (or, rather, the Tab).
Those last two options - INLINE logs and JFS2 snapshots - need to be set at the time of creating the file system. You can't changed either of them on an existing file system.
Mount options: CIO
For performance of Oracle databases, the file systems containing the database, control files and redo logs can be mounted using Concurrent I/O. The mount option is cio, but unlike the two previous settings (snapshots and INLINE logs), cio can be changed on an existing file system for its next mount. The CIO option takes effect when you mount the file system, so changing it requires unmounting and remounting for you to get the benefits of CIO. Turning it on ought to lead to a significant reduction in the use of paging space.