Networker

Re: [Networker] New server setup - VTL and LTO3 tape library for staging - best practices

2007-03-22 10:03:30
Subject: Re: [Networker] New server setup - VTL and LTO3 tape library for staging - best practices
From: Mark Davis <davism AT UWO DOT CA>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Thu, 22 Mar 2007 09:53:20 -0400
Brian,

I can help with one of your questions -

Brian O'Neill wrote:
OK, I'm about to embark on setting up a new Legato server to replace our venerable Sun 450 with P3000 library. It is my first adventure with a VTL, and using staging/cloning to any great extent.

I've read many posts regarding setting up VTLs, etc., and I just want to gather all of it and see if I've got it straight, and pose a few extra questions while I wait for the hardware vendor to plug it all in.

[snip]

Should I also set server parallelism to 16? I understand that regardless of device parallelism, it will add more sessions to drives if the server parallelism is set higher than the total.

Server parallelism of 16 would ensure no multiplexing with 16 devices. Networker will override the device parallelism if server parallelism is set higher.

I know this was to avoid multiplexing - but was this relevant to the VTL performance, restores, or was it more for staging later?

We just added another 16 virtual drives to our system to avoid multiplexing. It is a performance issue for restores and staging. Virtual tape behaves exactly like physical tape - if a saveset is multiplexed on a volume, the entire tape must be read to read the pieces of the multiplexed saveset you are interested in.

By minimizing multiplexing in our system, the speed of cloning/staging savesets from virtual to physical tape has gone up significantly. It is saving us many hours per day.

Note that you can add a storage node license to your server, without adding a storage node. This will allow you an additional 16 devices on your server, and the license is reasonably cheap.

One other suggestion I would make is keep your virtual volumes small if possible. Unlike Advanced File Type, you can only read the virtual tape one stream at a time. For example, if you are cloning the savesets from a virtual volume, and at the same time the volume is needed for a recover, the recover will wait on the cloning to finish. By keeping the tapes small, this type of problem is minimized. Our virtual volumes are set to 52GB in size.

Hope that helps.

Mark
--
Mark Davis
Legato NetWorker Support - I.T.S
University of Western Ontario
email: davism AT uwo DOT ca

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