Friends, I am learning the working of fssnap command.
Suppose there is a directory named /datadir which is of size 500mb.
I had taken the snapshot by means of the following command:
#fssnap -F ufs -o bs=/snapshotdir /datadir
{ it shows the o/p as
/dev/fssnap/0 }
My question is if I look at the size of /snapshotdir/snapshot0 file it is only in few KB.
But when I mount the /dev/fssnap/0 to some temporary directory its size is of 500mb and data could also be accessed.
Please clarify how this works...Can we say that fssnap can be used as a compression tool?
sorry if this is a stupid question.
fssnap is tool used to "freeze" state of filesystem, so it can be backuped. When snapshot is created it will contain image of filesystem like it was in time of creation. File you mentioned (/snapshotdir/snapshot0) contains backstore data that is needed for this purpose, like when you change some files in snapshotted filesystem, then original data is copied to the /snapshotdir/snapshot0, so it is possible to see old data when mounting /dev/fssnap/0. So when there are no changes done to filesystem, then there is no data written in /snapshotdir/snapshot0. As for mounting /dev/fssnap/0... It is mostly done by mounting unchanged data from original filesystem in read only mode, and then applying backup bits from backstore file when something changed in data after snapshot creation.