Re: [Networker] Networker Newbie

rrevuru AT GMAIL DOT COM wrote:

On 3/24/06, Peter Viertel <Peter.Viertel AT macquarie DOT com> wrote:

OK... Here's some answers to your questions....

Following are the questions
1. How come the "Used=Full" when it is not using the total capacity


of the tape

2. How come tape 1 can save upto 78GB and says it is full, tape2 can


save upto 49GB says it full.

Full - is a flag set on a tape to say - don't put any more on it...
Either someone has set it manually, or it hits end-of-tape, or the
system encountered errors on the device when operating the tape...
Networker will get fed up and mark the tape full... Even if theres
nothing wrong with the tape and its scsi errors on the drive.....

But most likely you are seeing the effects of hardware compression.
You don't mention your drive types or config - but that's another reason
for the variable capacity...   Some data compresses badly, some does
very well....




Can you tell me the what kind of compression ratio should i use to make use
of the maximum space on the tape. I am currently using LTO-Ultrium-2.

The compression ratio isn't something you can control - you get the bestthat your hardware can give.

When coming to compressing data . according to research i did so far,
compression is achieved from the client side (Networker User).

No this is just one way. You have a choice of compressing the data atthe client side, or letting the compression hardware in your tape drivesdo the work.

The advantage of client compression is most obvious when you are backingup over a very slow network. Less data is passed over the network. Thedisadvantage is that compressing on the client eats a lot of CPU andthis can sometimes have the effect of slowing the whole backup down ifthe CPU can't keep up with the amount of data that the network and thetape drive can accept.

The advantage of hardware compression is that most modern tape drivesare very good at compression and depending on the data you can sometimessee compression ratios of 4:1 or 5:1, sometimes even more.

It is not a good idea to use both software compression and also acompressed tape device because often the backed up data ends up largerwhen compressed twice.

Personally I always use compressed tape devices and extremely rarely usesoftware compression. The exceptions are when I have to backup over aslow WAN or sometimes when backing up to a disk device that is notcompressed.


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