Problem with backup!

[Ivakin Dmitry]

Hello All!

I have Windows 2000 SP3, NTBackup, HP Storage Works dlt vs80, tape DLTtape IV Data cartridge. I know that I can copy 40GB information in normal state and 80GB in compression state. My current backup set is 52Gb.
So, I created backup set, turn on hardware compression , but after somewhile I have message "The tape is full, please put the new tape". As I understand, the hardware compression in use, but anyway, the all information couldn't be copied to tape.
This problem already discussed, this is the path http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=226695.

May be, someone, could tell me the right solution to solve this problem? I'm alrady excluded some files from backup (I can copy them from other resources), but still about 53Gb can't backup. May be buy the new tape drive? If yes, which is recommended? May be some others solution. Please, help! Thank you!

[Kurt Beyers.]

Ivakin,

The data compression of 2:1 is only a rule of fist (a generalization after many observations).

The actual compression ratio is data dependent. Suppose you've got a database space file of 1 GB with only a few records of data in it. You'll achieve a very high compression ratio on this database file as it contains a lot of redundant information. But if the same database space file is completely filled with records, the compression ratio will be around 1.

So you are for sure that you can write at least 40 GB on a DLT800 tape and it is safe to assume that 80 GB of compressed data will fit on the tape. But the actual size that will fit on the tape can only be seen when the tape is full. A tape is always used by backup software till the end of the tape is reached.

You are noticing that the compression ratio is a bit lower than you would expect, but you can't do anything about it.

You could always do a test of your drive with the LTT software, so you can test the hardware compression as well. But it is data dependent and not a hardware problem.

best regards,
Kurt

[Ivakin Dmitry]

Thank you very much for your reply!

So, what is the right solution to solve this problem? I excluded as more as possible data from set, I can't exclude more. As I understand, the capacity of tape, which I'm using, can't be more than 40/80 Gb. The only one way to buy new device whith high capacity cartridges. Can you advice me, which one is better? Thank again, Dmitry

[Leif Halvarsson_2]

Hi,
Of course you can buy a high capacity drive (as SDLT or Ultrium) but you also need to buy new medias. Two (perhaps cheaper) solutions:

- Buy another vs80 drive and use two drives for backup.
- Buy a vs80 autoloader (for example C9264CB).

http://www.hp.com/products1/storage/products/automatedbackup/autoloaders/18series_tape/index.html

[David Ruska]

To check the compression rate of you backup set, you can install LTT 3.4, and generate a support ticket while the tape is still loaded (after the backup completes). The device analysis section in the support ticket will output the compression ratio.

[Ralf Loehmann_2]

Hello Iwakin,
there might be also another reason for not getting more Data on a tape. If you got a poor performance collecting the data and than sending them to tape it might be that the tape drive is filling gaps between your data. This is done by the firmware to keep the tape drive into streaming mode (this means the tape is moving all the time), because stopping and starting the tape motion will put a much higher wear on the heads (Tape and head life time is typically defined in passes and a pass is the change of movement over the head). So if you at that point you loose capacity just because of the poor performance and in addition you are reducing the life time of your tape drive and tape media. I also recommand that you check your drive and tape with LTT as descibed.
You might also try to use an backup application like Dataprotector (there are evaluation copies available, see: www.hp.com/go/dataprotector ) or something similar. Backup Application are better collecting the data and in addition they also making it easier to handle it.

Ralf

[David Ruska]

> If you got a poor performance collecting the data and than sending them to tape ...

The same device anaylsis I mentioned in LTT 3.4 will output the number of corrected write errors. More than a few hunderd per GB and you're capacity will be suffering.