Reserve / Release drives LTO/SDLT

[Noel Fernández]

Hi all,

We want to know if the HP drivers for LTO and SDLT (windows version) can reserve/release the drives. If a server in a SAN enviroment is working with the drive (do backup) and other server in a SAN try to access to the same drive during the backup...the drivers for windows block the second access?

IBM drivers for LTO can do it.

Thanks and regards.

[Curtis Ballard]

Reserve/Release isn't a simple question. It sounds really good but is actually quite complex.

You should start by looking at what backup application you want to use. Most of the time the reserve/release support is more a factor of the application than the driver. Many of the applications do reserve/release at the application level.

I can't say whether HP's drivers do reserve/release but I can say that doing it in a driver is dangerous in a multi-host environment.

I've seen a lot of backup failures reported as drive failures because of reserve/release conflicts. If you have the reserve take place in a driver but are using an application that supports multiple hosts being able to write and handles reservations itself then the application hands off control to a second backup server but the reservation doesn't get handed off and the backup fails.

Reservations also aren't a true "block access" feature. A fair number of commands are allowed through in the presence of reservations however the critical ones, read/write are blocked.

I strongly encourage the use of SAN zoning to control access to the drives rather than relying on reserve/release.

There have been so many weaknesses of reserve/release that it is actually obsolete in the SCSI standards at this point and has been replaced with a new "Persistent Reserve/Release" command. You can look at SPC3 at www.t10.org for more details.