mount snapof file system without refreshing...

[Doug Moloney]

We currently are mounting the snapshots with

mount -F vxfs -o snapof=/empi_interface /dev/vgsnap/lvol1 /snap01

and then unmounting them with
umount /snap01

I need to know how to mount the snapshot without it being refreshed with data from the /empi_interface directoy.

If I rerun the above mount command, it appears as if it is taking a fresh snapshot of the file system. I want to just mount the file system that had the original snapshot without refreshing.

Any help?

Thanks

[Sanjay_6 · Accepted solution]

Hi Doug,

the filesystem you create to use as anpshot does not hold any data. Only when you mount as snapshot, it contains the info for the filesystem for which it is mounted as a snapshot. Try this link for more info,

http://us-support2.external.hp.com/cki/bin/doc.pl/sid=5ad1461d096a1661d0/screen=ckiDisplayDocument?docId=200000006306354

http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B2355-90742/B2355-90742_top.html&con=/hpux/onlinedocs/B2355-90742/00/00/51-con.html&toc=/hpux/onlinedocs/B2355-90742/00/00/51-toc.html&searchterms=snapshot&queryid=20020208-104316

Look for "Backing Up a JFS Snapshot File System" in the second link. you don't create a filesystem on a snapshot lv. So you cannot mount it without using the snapof option.

Hope this helps.

regds

[A. Clay Stephenson]

Hi Doug:

Sorry, that dog won't hunt. As soon as you unmount the snapshot filesystem, the snapshot is gone forever. You see, vxfs snapshots don't work like you expect them to. They do not make a readonly copy of a filesystem but rather use the vast majority of the original filesystem that has not changed since the snapshot was made. The FIRST time a block is changed in the original filesystem, that block is first written to the snapshot buffer and then the update is made to the original filesystem.

To do your kind of snapshots, you need to do lvsplits.