Block size for adv_file device?

[goony]

On my Unix Networker server I can select the device (disk array 1TB) that is used as my adv_file device, then view Properties --> Advanced and read/set the "Device block size".

The HELP for that field says:

Device block size - This attribute describes the size of the transfers that are used when writing to or reading from this device. The value is set for a given volume when the volume is labeled.

Considering that this is a disk device, is there a particular optimal setting for this parameter... or is it best to leave it as "handler default"?

 

[605]

As usual, the optimal transfer rate depends on a lot of factors. You usually can only find the block size which fits best in your environment by running benchmarks.

 

[ess07]

I also have a question about block size. I was looking into changing the block size but I know you need to relabel your tapes afterwards. We have 12 week retentions on our tapes for restore purposes. If i change to a higher block size, can we still read the older tapes with lower block size? I was told yes they can read down but not up. Now the trick would be to relabel the tapes as retention lapses. Am i correct on this assumptions?

 

[605]

The block size is a drive parameter which has its impact on the media only after relabeling.

If you reconfigure the device's block size, you can always read the media as long as the system setup allows this (remember the usual 64KB border on Windows). As the block size is stored in the label, NW will inform you if there is a mismatch.

Just do re-label the media.

 

[Calippo]

Tuning the block size may indeed have a negative or positive impact on performance. In general, the larger the block size the better the performance, certainly true with tape technology.

Firstly you should refer to the NetWorker B2D best practise white paper for some foundational knowledge.

On your B2D LUN you should ensure that the allignment is correct (ie make sure you have the 63 offset set if using Windows). Then when formating the volume choose a block size of 64kb or 128kb for example, which you will match when you create the AFTD in NetWorker.

You will need to experiment with what works best for you because if the data you are backing up consists of main tiny files you may need to decrease these values.

All the best.