08-19-2008 01:51 PM
We have one library with a mix of LTO2 and LTO3 tapes. Our policies are set up so that the tapes that stay here are all LTO2. The tapes that go to Iron Mountain are all LTO3's. Is there a formula or a way to make an educated guess, other than past history, as to how many tapes will be needed? Especially over the weekend.
Thanks,
Maria
08-20-2008 10:01 AM
number of tapes is based on
how much you have to backup
how many drives you have
if you use compression
how many drives you have setup in your storage unit
how many concurrent jobs you allow ( the more you have and the more drives you have the more tapes it will use)
how many 'non full' tapes you allow per volume pool......
in other words... past history of how the backups did last time......
08-20-2008 11:27 AM
You can measure this based on the number of drives that you have i.e.
In an 8 hour time window:
1 LTO3 can backup 2.19TB
1 LTO2 can backup 0.96TB
This is the highiest number you can get in the best conditions so think that normaly all the environments are not in their best shape, but from here you can know which policies will use a kind of drives and which others will use the slowest one, with this you ensure that you are using your resources in the best way.
hope this helps.
regards
08-20-2008 02:51 PM
Just to add to the previous comments... take the following situation
5 tape drives (e.g. LTO3 with 400GB uncompressed)
10 clients to backup with a small amount of data on each (say 10GB)
You have set up all 5 drives to backup at the same time and you are not using multiplexing
In this scenario 5 clients will back up to 5 tape drives as the same time. As these finish the remaining 5 will backup to the same tape. You will land up using 5 tape and each will only have 20GB of data.
Take the same scenario above but have 50 clients with the same amount of data. Here 5 clients will backup to 5 drives. The following queued servers will start as the first ones finish untill all complete. Here you will land up using 5 tapes each with 100GB of data.
Basically, it is more about how you run your backups apposed to how much data you are backing up and you will have to find a happy medium between performance and costs depending on your requirements.
You can use the following to restrict the number of media used (you will have to decide based on requirements though)
1. Reduce the number of pools (especially for media being ejected)
2. Reduce the number of concurrent drives that can be used per storage unit
3. Reduce the MPF setting for your volume pool (Maximum Partial Full). In 6.5 and above
4. Remove tapes from the library less frequently. This will allow them to fill up more before being removed.
5. Create Server Groups that allow media sharing between media servers. (6.5 and above)
Other factors that increase your tape usage are the following
1. Multiple retention levels. These can't share the same media by default.
2. Multiple media servers. By default these do not share media.
Cheers