Originally posted by: SystemAdmin

what's the difference between inline log and the outline log in jfs filesystem?and what are they used for ?

Originally posted by: tony.evans

I assume you mean jfs2 since jfs doesn't support inline logs.

Outline logs are no different from old jfs logs, there's an LV on the disk which is formatted to be a jfs2log and the filesystem uses that. Multiple filesystems can use the same log.

Inline logs use up some space on the filesystem logical volume and don't have a separate device. Each inline log is tied to a single specific filesystem.

I've yet to find a definitive description of why you would choose one over the other with jfs2 (other than the very obvious points), but I'm sure this is the right place to get a good answer.

The obvious points:
Inline logs - less work required in creating them, filesystems are wholly contained and don't rely on another lv to be mounted, logs are dedicated to their own filesystems so don't suffer from being shared between filesystems.

Originally posted by: SystemAdmin

Many external logs sit on a single PV, even if the filesystem spans many disks.

If a filesystem uses an Inline log, and that filesystem spans multiple PV's, then you gain by virtue of the fact that the log is spread over more disks.

Originally posted by: tony.evans

> dial8d wrote:
> Many external logs sit on a single PV, even if the filesystem spans many disks.
>
> If a filesystem uses an Inline log, and that filesystem spans multiple PV's, then you gain by virtue of the fact that the log is spread over more disks.

Is that true? Does AIX spread the log PP's over the whole range of the LV or does it stick them all at one end?

Originally posted by: SystemAdmin

my understanding is that an inline log, being part of the filesystem is spread across the physical volumes that the filesystem is on.

Originally posted by: tony.evans

I agree it's part of the structure, but I've not read anything which says LVM will spread the inline log over the disks, it could just as easily choose to put it anywhere it likes (start or end of the LV).

Originally posted by: TeeraW.

Does the outline jfs log has any limitation?

For file system that has many files, does I should choose inline or outline jfs log?

Originally posted by: j.gann

the current oracle tuning on aix docs recommend using inline log (journal) for jfs2.

anyway: If setting up a new site or application I'd make the application people build a reference installation or workload first. Start with seperate log device. Use filemon while the reference workload is running. Will tell you important things about how hard the journal is actually being used (apart from other things like app read/write sizes etc....) As journaling only takes place on metadata changes it might be surprising how few IO the log device actually encounters. Even more so if constant-size data or container files are used.