First, thanks for the link back to my site about using iSCSI as a disk for Time Machine.
You can use the iSCSI volume just like any other attached disk to your Mac. You simply treat it as another disk and have to put HFS+ or other filesystem on it.
It is not necessarily true that the device must be disconnected to take advantage of snapshots. The disk (iSCSI volume) must be in a quiesced state where the are no writes performed to the iSCSI volume. If there are any writes when you are taking the snapshot, you risk data corruption or inconsistency. So, basically if there are no writes being performed, you may take a snapshot of the iSCSI volume and it should be perfectly fine when you mount it again if you roll back.
One of the biggest advantages of using ZFS for iSCSi on the Mac, especially if you are taking snapshots, is the data de-duplication. Each snapshot will take very little space on the ZFS side of things. Time machine seems to deal with files on the file level rather than the block level like ZFS. Though I haven’t tested this, it should work in theory.
I need to update my pages to use COMSTAR which is the latest OpenSolaris methods for accessing SCSI protocols, but just haven’t had time lately. I would suggest that if anyone is using iSCSI from OpenSolaris, they use COMSTAR rather than the older iSCSItarget which is what I am using in my instructions.
iSCSI is a very cool thing indeed. However, you cannot have two clients accessing the same iSCSI device simultaneously. This is just like regular SCSI devices. Each host will have it’s own internal cache and not be aware of what the other machine has written. As long as they access the iSCSI volume independently without the other accessing it, you should be able to use the iSCSI volume on multiple machine, just not mounted read/write at the same time.
Hope this helps.
Mike
