Networker

Re: [Networker] How NW cloning & multiplexing REALLY works

2007-01-23 13:35:50
Subject: Re: [Networker] How NW cloning & multiplexing REALLY works
From: Steven Weller <sdweller AT SBCGLOBAL DOT NET>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Tue, 23 Jan 2007 10:15:29 -0800
Correct on all counts.
NetWorker writes to disk as disk, using the AFTD, so you could max out your 
parallelism, (how many streams are actually sent at the same time), creating 
heavily multiplexed backups. However, the data will be placed on the disk as 
usual, in random writes. This is perfect for disk as when you read it can read 
in random so you automatically gain the demux when you read from disk.

This leads to the idea that using a disk target as your intial backup device 
and then clone to tape can create dramatically fast restores from the tape, not 
to mention the disk as well.

One of the things I left out on my earlier statement that Curtis' tests may 
have missed is that you can control the number of savesets that get multiplexed 
together by manipulating the parallelism on the NW server, as well as the 
client. If you set your parallelism to 1 and you have 10 savesets defined in 
the same client resource to be backed up, they will each get sent contiguously 
rather than concurrently, as Curtis' tests have shown. This in conjuntion with 
Target Sessions on your devices can help balance the load as well.

-S

----- Original Message ----
From: Dag Nygren <dag AT NEWTECH DOT FI>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Sent: Tuesday, January 23, 2007 9:03:35 AM
Subject: Re: [Networker] How NW cloning & multiplexing REALLY works


> >
> >Why couldn't you do parallel reads from the disk?
> >  
> >
> In theory this is possible, but in current versions it is not written 
> that way. You can only read one stream from a disk device at a time.
> 

Correction to my last mail:
The parallel recoveries were introduced in 7.3 not in 7.3.2.

Best
Dag

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