8 Krypton

Save sets and sessions

Folks,
I have questions..

1. Does each save set takes one session for backup? If my target session is 2, that means, i can only backup 2 save sets at any one time, right?

2. Let say, there are four save sets from one client. And there are two tape drives. Target session on each tape drive is two. Does it mean that the save set from this client goes to two different drives, two each?

TIA
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4 Replies
8 Krypton

Re: Save sets and sessions

Hi,

1. Does each save set takes one session for backup?

Yes, each saveset generates a savestream (session)

If my target session is 2, that means, i can only
backup 2 save sets at any one time, right?

No, target session is a device parameter that means how much sessions one device can take before Networker try to use anoter one. If all other devices are busy too, Nw will start to balance new sessions in all devices, until max sessions or server paralelism is reached.


2. Let say, there are four save sets from one client.
And there are two tape drives. Target session on each
tape drive is two. Does it mean that the save set
from this client goes to two different drives, two
each?

Yes, one device will get 2 sessions, target session was reached, so Nw will send next ones to the other device. If 2 other savesets come, Nw will send one for each device.
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8 Krypton

Re: Save sets and sessions

what is the optimum/best/safest number for max parallelism in networker server before it is overloaded? anyone has experience to share?

i am looking at effectively managing the tapes, SN and servers...

thx again...
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8 Krypton

Re: Save sets and sessions

Hi,


The answer is "it depends" ...

It depends on what you are backing up to the tape and more importantly what your recovery needs are.

My colleagues and myself normally set device streams to one - no multiplexing when the backup data is coming from high speed storage devices, straight across fibre channel to storage nodes. However, if the backup data is LAN based or from slow clients then you need to experiment with you setup to optimize the device transfer / write speed. But, and there is always a but, the more data is multiplexed to the tapes the longer the recovery time can be.

Add to this mix the third party backup protocol used by NDMP which is a single stream protocol then you need to find what's best for your environment.

I would suggest that the fewer the levels of parallelism used the better - also with NetWorker 7.3 / 7.4 there are some recommendations from EMC that you set server max parallelism higher than the total number of devices times the number of device streams set.


HtH

IKP
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mfriedma
6 Indium

Re: Save sets and sessions

The best way to describe the optimum number of savesets per tape is quite easy.

Use the minimum number of savsets necessary to achieve or exceed your drive's MTR (Minimum Transfer Rate -> which is not by all means the native throughput of the drive as stated by the vendor).

Of course there are many parameters that may affect the result such as available bandwidth of the LAN/SAN, the abililty of the client to push data at a specific rate, etc...

Therefore, the only educated recommendation I could share with you is test your environment and find your bottlenecks. You could face a very fast bottleneck but it will determine the maximum obtainable performance achievable in your system.

HTH
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