Determining Tape requirements

Snafu

ADSM.ORG Member
Joined
Jun 4, 2010
Messages
28
Reaction score
1
Points
0
PREDATAR Control23

Hi

I'm working on my first TSM deployment and so far everything is going great, except I can't find any information on determining how many tapes I require. Is there some sort of calculation I can make based on how much is getting backed up nightly, compared to the size of media being used?

Thanks
 
PREDATAR Control23

I find to determine the amount of tape needed is not an exact science; however, there are somethings to be aware of to help you get a feel for how many tapes you need.

A few questions you need to do your best to find out:
How much data will be protected?
How many versions will be kept?
What percentage will reclamation be ran?
How long to keep the tapes empty before overwriting?
- aka This allows you to roll back TSM and still have the data on the tapes.
Any collocation going on?

A simple example:
(note LTO4 is 800GB or 1.5625 TB compressed @ 2:1 ratio)
I have a node that will have 1 TB of data to be backed up.
I want to keep at most 31 days or 10 versions.
I have LTO4 tapes, which is 800GB or 1.6TB compressed - I choose compression.
I want a tape 60% empty to reclaim.

1TB (worst case if it changes daily I will hit the 10 versions before 31 days) I will have 10TB including versions. I will need minimum of 7 tapes (1.6TB * 7 = 11.2TB) just for the backup. Now if I want a copy off site then, another 7 tapes. However, don't forget the data will expire... so as the data begins to expire, when do I want to reclaim the tape? 1.6TB that is only 40% full (or 60% reclaimable space) is really .64TB so up the tapes from 7 to 16 tapes for each tape pool.

Now I am at 16 tapes for each pool, 32 in total just for the data needs. Add about 10% to 20% (32* 20% = 6.4 or 7 tapes) for scratch volumes; up to 39 tapes. Now TSM 'reusedelay' as well collocation (I recommend googling those terms if you have questions) will increase the amount of tapes needed as well as other settings I failed to mention (in my defense this is off the top of my head). Math may not be entirely accurate but gives a good idea of what to look for.
 
PREDATAR Control23

I always based it off of the full+((average daily % of change*full) * days retained) so if a full for the environment is 23TB and average daily change is 10% and you will keep data for 31 days (usually I've kept as many versions as days kept) then:

23+((.10*23)*31) = 23(2.3*31) = 94.3TB

if you get 1.5:1 compression on LTO4 (800GB * 1.5 = 1.2TB) then you have 94.3TB / 1.2TB per Tape = 78.5 tapes if you consider scratch and yearly growth in then I would order at least 90 to 100 tapes (100 more than likely).

Note that I don't use IBM's 2:1 compression since I have not seen that level of compression on heavily windows locations but have seen 2:1 or better with UNIX and DB backups.
 
PREDATAR Control23

Is that 100 tapes overall? Meaning does it cover your on-site tapes and off-site copies?
 
PREDATAR Control23

Doh! No it doesn't cover offsite. My memory must be going with old age. Another thing to ask is "Do you plan to use collocation onsite?" If you do then will it be node or group? This will also add to the # of tapes you use. Use the previous calculation for offsite since most people don't collocate offsite and if they do they use group. To determine onsite you could use that formula and double it for offsite, but with collocation (which I hope you use) you will add to the overall tape useage. So how many nodes are there and if you plan on collocating by group, how many nodes will be in a group?
 
Top