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Increasing "Number of Data Readers" effect Throughput for Tape Copies?

vqt411 (IS/IT--Management) (OP)
24 Oct 06 14:20
Hi All,
Our backup strategy is going D-D-T. Does anyone know if increasing the "Number of Data Readers" and "Allow multiple data readers within a drive or mount point" when backup up to disk will degrade network Throughput once it goes to Tape? Thanks in advance.
birky (ISP)
25 Oct 06 9:24
If using multiple streams to your primary disk then you would have more data being transfered to the tape media and you would use more tapes as each stream writes to it's own drive/media.

To prevent this you could enable multiplexing or 'combine streams' on your aux copy to tape.
vqt411 (IS/IT--Management) (OP)
25 Oct 06 13:06
Thanks birky.  We are utilizing multiplexing and combine streams for our aux copy.  We currently have more disk space than we do tape drives to aux copy them.  We are in the process of purchasing more tape drives to accommodate the increase in backup data to disk.  I just noticed that the aux copy Throughput has degrated over time.
BkpAdmin (IS/IT--Management)
9 Nov 06 15:59
Multiplexing adds signifigant restore time.
birky (ISP)
10 Nov 06 5:19
Usually yes, multiplexing adds to restore time but, it says in the online docs that multiPlexing with Galaxy doesn't  because of the indexing structure of Galaxy so there isn't so much seek time.
BkpAdmin (IS/IT--Management)
10 Nov 06 13:51
if you are doing a job based restore you will not notice any or very little latency from seeking because all the data from the backup is tossed back on the disk.

That being said - if you select files from the browse in all different file locations you will definitely see the effect on recovery time.

Even with the indexing structure you are still striping your tape.

example - If you have Multi Factor of (4) That means you are striping 4 jobs to the same media at once. So you need to read through (3) insignificant jobs to get to the next chunk of wanted data.

Restore of Job ID 1:
*               *               *
1 - 2 - 3 - 4 - 1 - 2 - 3 - 4 - 1

And that is for job based restore - when performing file level restores you will notice a bigger performance hit.

Speed on the backup vs. Recovery time has always been the bane of multiplexing and tape media.

This is my understanding anyway smile

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