Maximum size for 1.6TB Hp LTO Ultrium Data cartridge

[raju_tamang]

Dear all,

I am using a 1.6TB Hp LTO Ultrium Data cartridge I would like to know what would be the maximum size I can have after formatting the cartridge since i have a problem taking backups as my data size is abt 130gb everyday hence i cartridge lasts just for about 4-5 days

thanks in advance

[thomasr]

I'm not sure exactly what you're asking, but I'll try to answer.

The native capacity of an LTO-4 tape is 800GBytes - that is, 800,000,000,000 bytes.    If your data is compressible, much more can fit on that tape -- but it will still only be 800GB actually written to the tape.  Remeber, though, that each file written also requires some metadata to be written with it -- file name, directory path, all the file attributes such as creation data, last modified, owner rights, etc.   These can take up a significant amount of space compared to the file itself, particularly if your average file is small (and a huge percentage of general-purpose server disk is files under 10K, and even under 1K.

Also, if you let the tape drive buffer empty, it has to stop writing, rewind, start going forward again to find where to resume, and and then start writing again.  Unfortunately, there will be a gap between where writing stopped, and where it starts again.   If there are a lot of stops and starts, this could chew up a lot of space.

Also, dirty heads or degraded media can cause a lot of rewrites, which will also chew up space on a tape.

So -- 

- Make sure you're getting data to the tape fast enough (this will be at least (native speed times compression divided by two).   Native speed of a full-height LTO-4 is 120MB/second; if your data averages 1.5:1 compressibility, the speed you'd need to feed your drives is 120 * 1.5 / 2, or 90MB/second  (you might be able to get by with a slightly larger divisor, but since data is not uniform on a disk, 2 gives a bit of headroom, maybe).

- If you can't feed your tapes data that fast, you could consider turning off compression, which will help you achieve more streaming and less buffer under-run.

- Use cleaning tapes as indicated

- Ensure you are using high-quality media.

And of course, the absolute guaranteed way to fit more data on the tape is to perform a full backup just once a week, and differential (my  preference) or incremental backups the other six days.    In this way, you might easily fit three weeks' worth of data on one tape -- but realize you're at great risk of losing three weeks' worth of data should your server fail at the same time you lose that one tape (earthquake, fire, theft, flood, ....).

So you start some sort of tape rotation -- at a minimum, two backup tapes, each one gets used for a week for full + differential backups, and then taken offsite, while the other tape is brought in to have a full backup plus the differential backups for the rest of the second week, then swap again for week 3.