OpenSolaris, ZFS, iSCSI and OSX - Creative Storage - Part II
At the end of the last post I left off on the part dealing with configuration of the iSCSI initiator side of the solution. I stopped here because there were some issues related to the installation and use of the software.
The iSCSI initiator that I was using was Studio Network Solutions GlobalSAN initiator (version 188.8.131.52) which is used to allow for connections to their products. This software will also allow for connections to ANY iSCSI target!
After the configuration of the iSCSI target on the ZFS pool, and installation of the client it was trivial to get the connection established with the storage pool, and it showed up in OSX as a raw disk which had not been formatted.
I proceeded to format the disk as HFS+ and it then mounted as a locally attached disk and I was able to use it as a target for the Time Machine backups. Once selected OSX nicely backed up all of my data to the volume! Perfect! Even the performance of the solution was suprising, as it appeared to significantly outperform previous backups made using USB disks attached to an Airport Extreme, and all of this over my 802.11n network!
Main Problem: Disconnections. Everything worked really well for me if the wireless network connection was active, the iSCSI client was properly started and connected, and Time Machine backups were closely monitored. While this will likely work really well for the guys with hard-wired gigabit connected Mac Pros that are never disconnected from the network or turned off, my MO includes constantly connecting and disconnecting from the network, and also in the middle of performing TM backups.
These disconnections immediately started causing problems with both the iSCSI client connections with the ZFS pool, and with the Time Machine processes associated with the disk. Symptoms included strange errors regarding mis-matches between the sparse disk images and the connected volume, and reconnection issues with the iSCSI client when my laptop gets reconnected to the network without stopping and restarting the iSCSI client.
Solution: CIFS. I always believe that simple solutions are better than complex ones, and although being able to use iSCSI connections to establish disk access seems cool, it doesn't offer a whole lot over standard-old network attached storage. The main reason behind the iSCSI configuration was to get TM to work with the ZFS pool, but there is an alternative - CIFS. There are many posts around the net regarding the use of CIFS and SMB shares for Time Machine backups.
So what I ended up doing is configuring a single ZFS pool for storage and splitting this storage into two - one for general file storage, and one for backups. TM uses sparse disk images which provide the added benefit of limiting the size of the disk image (this is used to limit the amount of disk space which is used by the TM backups - currently 2x the size of my source disk).
By using CIFS as the access method, I also have the ability of backing up my Windows boxes to the same filesystem along-side the TM disk images for each OSX machine.
In part III - when I get time, I will hopefully post the details on the CIFS setup (including security and file permissions), the OSX TM setup, and the Windows backup settings.
I have been using this setup for a few weeks now without a hitch and I have also restored files over the network. The only thing I haven't tested is restoring a full osx install from install DVD's using the TM backup (plan to test this).