On Dec 1, 2006, at 5:42 PM, Sean Murphy wrote:
Thank you for your knowledge on this issue. I have a few questions that I need your help to clarify.

You are welcome, although knowledge can be a tricky thing.  :-)

"Snapshots are taken via mksnap_ffs; some other tools like fsck or dump also know how to create a snapshot."

OK, so if I understand this correctly I do not have to initially take a snapshot and update this snapshot manually. The files system with soft updates does it correct?

If the system is rebooted with a filesystem which is marked unclean, and if soft updates is enabled, then yes, the background fsck process will create a snapshot automatically, and not need manual intervention.

"Maybe. I think that softupdates is a win in almost all circumstances from the standpoint of data consistency, short of fully syncronous data & metadata updates."

On this issue, if I do not have soft updates on does that make it a fully synchronous file system?

No. Take a look at the manpage for "mount", in particular the section on -o which discusses async, sync, and noasync. The latter is the default:

"             noasync
Metadata I/O should be done synchronously, while data I/O should be done asynchronously. This is the default."

If the background fsck can't handle the inconsistencies it will report this in the /var/log/messages correct? Then is the file system unmounted because of the inconsistency to prevent data loss, so I can run a manual fsck or does it stay mounted?

It should fall back to running a foreground fsck instead, which might indeed require manual intervention, I believe.


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