In many installations it's a close to meaningless number. For empty tapes, it's the estimated capacity of the tape multiplied by maxscratch. Then as tapes become full, the actual number of bytes written will modify the estimated capacity value. The actual bytes written depends on compressibility of the data. The reason why in most of my installations it is a meaningless number is that tape libraries are managed by the number of scratch tapes available. I generally suggest that there should be about 10% scratch tapes in a tape library or at least five (five is also the threshold value for attention grabbers in the TSM v5 Operational Reporting Facility). Tape storage pools are then not restricted by the number of scratch tapes that may be assigned. Very often maxscratch is set to 10000 or some such number. You will often find large maxscratch values also in server-to-server virtual volume environments where the maximum capacity in most cases is set to be significantly smaller than the capacity of, for example LTO3 or LTO4 tapes.
Note that for device class disk storage pools the estimated capacity is the actual capacity. Joerg Pohlmann 250-585-3711 -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[email protected]] On Behalf Of Mehdi Salehi Sent: Friday, July 09, 2010 08:06 To: [email protected] Subject: [ADSM-L] tape stg capacity Hi, How is tape storage pool "estimated capacity" calculated? I see different values for similar storage pools of the same devclass and maxscratch. Thanks
