Solaris: virtual slices/disks for use with ZFS

Question

This is a little related to my previous question Solaris: Mounting a file system on an application's handlers except this question is for a different purpose and is simpler as there is no open/close/lock it is just a fixed length block of bytes with read/write operations.

Is there anyway I can create a virtual slice, kinda like a RAM disk or a SVM slice.. but I want the reads and writes to go through my app.

I am planning to use ZFS to take multiple of these virtual slices/disks and make them into one larger one for distributed backup storage with snapshots. I really like the compression and stacking that ZFS offers. If necessary I can guarantee that there is only one instance of ZFS accessing these virtual disks at a time (to prevent cache conflicts and such). If the one instance goes down, we can make sure it won't start back up and then we can start another instance of that ZFS.

I am planning to have those disks in chunks of about 4GB or so,, then I can move around each chunk and decide where to store them (multiple times mirrored of course) and then have ZFS access the chunks and put them together in to larger chunks for actual use. Also ZFS would permit adding of these small chunks if necessary to increase the size of the larger chunk.

I am aware there would be extra latency / network traffic if we used my own app in Java, but this is just for backup storage. The production storage is entirely different configuration that does not relate.

Edit: We have a system that uses all the space available and basically when there is not enough space it will remove old snapshots and increase the gaps between old snapshots. The purpose of my proposal is to allow the unused space from production equipment to be put to use at no extra cost. At different times different units of our production equipment will have free space. Also the system I am describing should eliminate any single point of failure when attempting to access data. I am hoping to not have to buy two large units and keep them synchronized. I would prefer just to have two access points and then we can mix large/small units in any way we want and move data around seamlessly.

This is a cross post because this is more software related than sysadmin related The original question is here: https://serverfault.com/questions/212072. it may be a good idea for the original to be closed

Answer 1

It seems that any fixed length file on any file system will do for a block device for use with ZFS. Not sure how reboots work, but I am sure we can get write some boot up commands to work that out.

Edit: The fixed length file would be on a network file system such as NFS.

Answer 2

One way would be to write a Solaris device driver, precisely a block device one emulating a real disk but that will communicate back to your application instead.

Start with reading the Device Driver Tutorial, then have a look at OpenSolaris source code for real drivers code.

Alternatively, you might investigate modifying Solaris iSCSI target to be the interface with your application. Again, looking at OpenSolaris COMSTAR will be a good start.