Collocation

[BenAd]

Hi,



I am new to TSM and would like some infomation with regard to Collocation.



I have been told that turning this setting ON will aid faster restores (for DR) but I am worried about the knock on effect it may have on the backups. I have 4 lto drives available and around 40 servers to backup, so the drives are in use nearly all day anyway( including housekeeping etc).



Any info. would be most welcome.



Thanks

 

[pbanghart]

Four drives...forty clients...hmmmmm...



Depending on the amount of data being backed up (which translates to the amount of time the tape will need to be on the drive), collocation may not be a good choice "across the board".



I have heard arguments both for and against collocation, but the bottom line is where you want to pay the price, either stretch out your backups and set up for expedient restores, or vice-versa.



I might suggest prioritizing which of the 40 servers really needs to be restored faster than others and seperate those into their own management class or policy that has collocation turned on...then see how it goes and build from there.



Sorry I don't have a definitive answer, but I hope this helps...

 

[heada]

The Theory behind co-location as I see it as follows:



do your backups to primary diskpools

at the end of backup day, backup the diskpool and then migrate contents of the diskpool to a primary tapepool. The migrate could take along time since this is when it has to mount a different tape per client.

The Primary tapepool is colocated so all client data is on the same tape and your diskpool is now empty for the next day's backups



restores will now run faster since less tapes will be mounted.

backups should not slow much if you backup to disk. If you do not have the primary pool as disk, then backups will slow ALOT since it will mount a tape per client.



-Aaron

 

[cwalden]

Your assumption of how collocation works is correct. There are two other points you should consider: backup is pointless without being able to restore. This might seem like just common sense, but your backup infrastructure should be designed with maximum restore capability possible given the budgetary constraints of your environment. Once you have documented your service level objectives/agreements on how fast things have to be restored, then you can design effectively. Most folks these days have a very diffucult time getting the managers to buy more equipment, but if a critical restore comes along and your infrastructure won't do the job, guess who gets blamed? Plan for restore capability (which means using collocation judiciously), then design accordingly. Maybe you need more tape drives or a bigger disk pool...



Next point: you don't necessarily have to keep your collocation level down to one client per tape (or set of tapes). Use the 'maxscratch' value to drive up the utilization if necessary. In your example, you could set maxscratch to 20, and your 40 clients would end up using 20 tapes (assuming that they all have less data than will fit on a tape of course). If those 40 clients each only back up 2GB of data, they would all fit on one tape without collocation.



Just my $.02