Why the backup capacity not fully used? 1

[phoenixlu]

Hi,I have a problem in backup the exchange server recently.
My back up tape size is 50GB, but for this week, it always asking me to "remove the media from the drive and replace a new tape " when the back up come to around 28GB.I am so curious why I must replace a tape since there is still 12 GB left. Could anyone help me out? Or anyone can give me a suggestion how to check the size for my backup tape by ` VERITAS: Backup Exec`? Thanks a lot.

 

[PerryMc]

I believe it's to do with how compressible your data is. We back up to dlt iv tapes that can theoretically hold up to 80Gb using hardware compression. They manage about 64 to 68Gb off a Windows NT4 file server.

Smile anyway,
Perry.

 

[evonne]

Hi there,

We have this problem so I contacted Vertias. The answer Perry gave is what Vertias told me.

 

[phoenixlu]

THanks a lot for your information,Perry and Evonne.But I am not sure what do u mean by the compression of the data,because the data is updated daily so it is backuped uncompressed. So can anyone tell me what shall I do to fully use the back up tape size?
Thanks.

 

[2ffat]

The compression is done either by the tape drive or Veritas depending on your settings. Look at BE's documentation on how to check which you are doing.

Now look at your tape. It will have a rating like 25GB/50GB. This means the tape will hold 25 GB uncompressed with 50 BG compressed data. In rating the tapes, manufacturers use the best-case scenario where data is compressed 2:1. In reality, this rarely happens. At best you might get 1.6:1 compression with common ratios of 1.2:1. It depends on what you are backing up. Data files and word prcessing file will compress more than executables, for example.
James P. Cottingham

When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute and it's longer than any hour. That's relativity.

[tab][tab]Albert Einstein explaining his Theory of Relativity to a group of journalists.

 

[phoenixlu]

Hi,thanks for ur info. I have checked,for the back up job definition,I already set the compression to `Hardware(if available,otherwise Software) in Veritas.But how come I still can only backup up to 30GB with a 50GB tape?Is that because I can only get 1.2:1 ratio?

 

[Qdog]

You will never hit the biggest capacity rating of your tapes as indicated by the previous posts. That said...see if there is updated firmware for you tape device(s). If you are using hardware compression, Backup Exec merely hands that whole compression process off to the hardware. So therein lies the answer. If you are using the latest firmware for your device, consider reapplying the same firmware version again. It is possible that the firmware is corrupted, which could cause compression to either fail or not complete properly. Look at your job logs to see what type of compression was enabled. If it was hardware, unfortunately it will not tell you what the ratio was (because it is handled by the firmware!)
Hope this helps. Take care.