Tim,
If someone gave me 48 TB to backup, on one contiguous drive, I would definitely do the spanning thing instead of micro-managing the tape backup.
How we get data is one of two ways.
During shooting each shoot day creates, 400 GB- 1.5 TB of data. This is sent to us on drives of 3 or 4 TB either daily or couple of times a week. We backup data and send back the drive and the tape to be kept at different locations. So, if the data is less than one tape’s worth, we either don’t start backup unless we have at least 2 TB, or just backup anyway depending on schedule. So, data is received in about 2 TB increments.
Later, if at all the production has any issue with the hard drives, we are called upon to restore specific day’s data. For this, there has to be some way for the human at the other end to pull out the specified tape to send back. And that’s labelled so its easy. A spanned data set would mean we have to ship all tapes in that set, right?
Second, sometime we need to backup an entire film’s data of, say 52 TB sent all at once. This 52 TB is spread over, say, 6 RAIDs of 10 TB each, or often 19 drives of 3 TB each. So, while its possible to span each RAID of 10 TB, spanning drives of 3 TB into ‘mini-sets’ of 2 tapes is also wasteful. The drives themselves have anything like 2.3 to 2.8 TB data on them, usually stored day-wise.
So, backing up day-wise and letting space go ‘in the end’ of each tape is the easiest solution for labelling, storage and restore.
We often need to restore specific shots form these tapes, or specific sounds. These are specified to us by file name and date of shoot. So tracking back the tape is easy. Particularly since the tape may be stored at a faraway location.
I know a lot of this can be fixed by using barcodes instead of human readable labels, but most of the LTO storage locations are private offices or homes and don’t necessarily have that facility.
But one question. Supposing I did backup 48 TB into one set of, say 21 tapes. And send off the tapes and drives.
Later, if someone asks me to restore a specific file or folder, can I restore with only the concerned tape/s? Or do I need the entire set of 21? This is significant because backup tapes are often shipped out to faraway locations, so shipping back would be required.
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Neil Sadwelkar
neilsadwelkar.blogspot.com
twitter: fcpguru
FCP Editor, Edit systems consultant
Mumbai India