Streaming

[uadmin]

Hi

I am running Networker 6.1.1 on hpux 11 and would like to now is it possible to stream two tapes at the same time hence improving performance.I now this is possible with NT so surley UNIX can manage this as well.

Regards
Simon Simon Peter Wickham
Email: s.wickham@zoom.co.uk

 

[MoshiachNow]

Hi,

1.Normally it's possible to save multiple sessions per device - say,setting "session per device " to more then 1 (default).This writes to 1 tape at a time.

2.Eventhough it improves backup speed,it slows down the recover.

3.Think of an emergency recover situation - it may be a bigger problem to locate 2 tapes,and still to locate 1 saveset written to both.


Basically,I do not like the idea. "Long live king Moshiach !"

 

[uadmin]

Thanks for the help i think we will look at getting a couple more drives in place.

Regards
Simon Simon Peter Wickham
Email: s.wickham@zoom.co.uk

 

[uadmin]

Hi

is incresing "session per device " the same as in
Devices- Target session.

Other wise where does this option lie.

Regards
Simon
Simon Peter Wickham
Email: s.wickham@zoom.co.uk

 

[mgdaviso]

We have 2 x 3590 tapes on a sun E450 that allow up to 16 target sessions per tape device, and we never have any problems with recoveries. Depends on the type and speed of your tape device really.
If target sessions is set to 1 that means you can only back up ONE volume/filesystem at a time, which is inefficient as the tape drive must stop/start in line with the buffer flush of data from the server. If you have another number (only found by trial and error and checking your throughput stats) in our case 16, you can have 16 sessions maximum all writing data to the tape at once, so in effect the tape drive is kept moving (hence "streaming&quot and therefore not stop/starting. Like levw said it decreases backup time, and increases recovery time, but that depends on how often you need to recover. We don't find it to be a problem.
HTH Mike davison
mike.davison@avon.com

 

[ulsj]

Hi!

The target session per drive is only a guid to get youre drive streaming. The drives will accept more session. If the server is handeling say 10 sessions(paralellism) thees sessions will be spread to all drives. On NT the default target sessione per drive is 4.

Example: server paralellism is 10 you have four drives
drive1 target session 2
drive2 target session 3
drive3 target session 1
drive4 target session 2

If we dont count with access weight it would look someting like this. The first two session will go to drive1 and session 3,4,5 on drive2 and so on to you reached 8 sessions the ninth session will end up at drive1 and the last session on drive2.

I usualy use target sessions to get a good load on the drives

Please correct me if i´m wrong.

 

[uadmin]

Thanks for the help i will try this.

Regards
Simon Simon Peter Wickham
Email: s.wickham@zoom.co.uk

 

[stol12]

Hi,

We have experimented with target session and found that 3
is a good number if you want restoretime to be almost like backuptime. Of course you have to make sure that the number of drives * targetsession equals server paralellism.
Target session is just a recommendation, if there is server paralellism left when all drives has 3 sessions, each drive will get more sessions until the server paralellism has been reached.

Regards,

Staffan