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Questions about jfs2 log.

Posted on 2013-01-29
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Last Modified: 2013-01-29
OK, here he go wmp..

1- Which is better to use, INLINE or JFS2LOG?
2- Is possible to see the usage of the JFS2 log lv?
3- What happen if I umount a /filesystem, logform /dev/hd8 and mount /filesystem? The data is lost?

Not clear at all about how JFS2 log works..;)
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Question by:sminfo
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woolmilkporc earned 500 total points
ID: 38831525
Hi, and welcome back in our new year 2013 - hope you had a good start!

1) Hard to say. Some people prefer having a distinct log per filesystem, and with this setup an inline log is much easier to handle. With inline logging there is a distinct log per FS by design, no need to create lots of new logvolumes.
On the other hand, if you have an FS with heavy metadata activity (create/delete/update) you could consider using a separate logvolume on a separate disk for performance reasons.
Anyway, a logvolume should be mirrored if feasible, and an outline log can have multiple copies even if the original FS is not mirrored (well, a rare scenario, I assume ...).
If an FS with an inline log is mirrored the "log" part is automatically mirrored too.

I, for one, tend a bit more to inline logs ...

2) If with "usage" you mean "filling level" - no you can't see that. Only the FS itself is aware of what is placed where in the log volume.
If you mean "activity" instead - this can be monitored with "lvmstat" just as any other logical volume.

3) Formatting a log with logform destroys the log records contained therein, regardless of the log type used. Formatting an outline log volume means reformatting the whole volume, running logform against a filesystem volume containing an inline log means reformatting only the "log" part of that volume which doesn't affect filesystem data.

A filesystem journal keeps track of changes to metadata, such as the superblock, inodes, pointers, directories. In case of a filesystem crash the information contained in the journal is used to recover this metadata.


wmp
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Author Closing Comment

by:sminfo
ID: 38831683
here I am wmp.. as always, with my topas at 100% USED...;)

OK, I understood everything.. thanks...
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Author Comment

by:sminfo
ID: 38831698
BTW, do you have EMC storage there? I have a problem (case on IBM now) about mksysb of LPATRs and the EMC's powerhdisks and multipath.... tell me and I open a new question...;)
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by:woolmilkporc
ID: 38831889
Sorry, no EMC anymore. And even in those old days we never had a rootvg on it.
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Author Comment

by:sminfo
ID: 38832337
heheh... I'm suffering with this )*(&*)()&PJM EMC.....:-(

see ya!
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