Thursday, July 07, 2005
FYI: Using Mixed Media In An LTO Library
We recently upgraded one of our 3584's at work with some LTO2 drives. This is the first attempt at a mixed media environment and according to IBM and the following Redbook technote here, you must work out the issues with MOUNTLIMITS or all LTO2 drives could end up in use when you need them since they can also read LTO1 media. So we set our mountlimits accordingly, but it does not help that we have more LTO1 drives than LTO2. So by setting the mount limit to the number of LTO1 drives didn't stop TSM from accessing the LTO2 drives. This they did not explain well and they left one crucial piece out of the puzzle. When using a mixed media library if you do not specificly state which media format to use TSM will use both LTO1 and LTO2 media in a LTO designated storage pool. You want me to explain further? Ok here is how it affected us. We added LTO2 drives and an additional 2 frames to our library and setup the devclasses accordingly, setting the FORMAT to DRIVES so it would use the highest format available by the drive assigned. Well since we didn't partition the library TSM is going to grab whatever drive comes available and will mount the appropriate scratch tape. So if TSM assigns an LTO1 drive then you'll use an LTO1 tape. The only way you can force the LTO2 media to be used is to set the FORMAT setting in the devclass to ULTRIUM2 or ULTRIUM2C (w/Compression). So we didn't think about that and were bit by it when we ran out of LTO1 scratch. We didn't catch it due to our script only looking for scratch in the library not being able to designate between the two media types (which you can really only do if a different vol series is used for labeling). So without the LTO1 scratch we basically lost 2/3 of the drives and didn't know it. So I had to go switch our script to monitor both scratch types and we had to force the LTO's to their appropriate format. Once I realized what was happening it was a "NO BRAINER" that TSM would work that way. The big problem is that TSM did not seperate out the media format for LTO2 so it would be a different devclass type like they did with the 3592's. So be aware how TSM works and make sure you don't make the same mistake I did.