back up the data?


--------------------
William M. Fennell
UNIX Administrator
Channing Laboratory



Ernst Bokkelkamp wrote:

Your message needs a bit of rewording:

Our SERVER parallelism is at 40.
Three tape devices are configured for 4 TARGET sessions and the other two
are configured for two TARGET sessions each.
If we are at generating 16 streams using all of our tape devices,
parallelism will
exceed the configured target session maximum and keep going up until 16

sessions are running.

Server parallelism: Max number of sessions a server has been configured to
be active at the same time. Please note that the real limit depends on your
license and the number of storage nodes that have been configured (see the
manual!).
Target setting: This is the number of sessions per tape drive before the
next drive should be selected. However this is not a limit!

Btw: You should target the minumum number of sessions to keep your drives
spinning. It is bad practise to overload the drives with sessions, altough
it doesn't make a difference it the only thing you do is backup and never
intend to restore!. The reason for targetting the minimum number of sessions
is easely explained: Just assume that you are backing up 16 clients with one
saveset of 200 Gbyte each to 4 drives, each with target sessions set to 4
and server parallelism set to 64.  Running all sessions at the same time
will cause each drive to hit the target level. Now if each client can
generate sufficient bandwith to produce half the bandwith of a tape drive
then you will need double the time for each client to backup all the data.
But if you reduce the server parallelism (8) and target sessions (2) so that
only half the clients can be active then each client will only use half the
time and you can do all the backups in the same time. Does this make sense ?

However, looking at restore, the target sessions can have very detrimental
effect on the time needed. If you assume that the client is capable of
taking up everything the tape drive can be delivered then the time to
recover will depend on how fast the tape drive can move the tape
(inches/second). Lets assume that the drive can move the tape, while
reading, from beginning to end in 1 hour, then it will take one hour to read
all the data on the tape.
Now if one tape cartridge has a capacity to backup one client, then you will
need n cartridges if n clients are backed up to the same tape drive with
target sessions set to n and will run for n hours. This means that you will
have to read n cartridges, or n x the tape length, using n hours to restore
all the data on the client. This means that the restore of 1 (ONE) client
will take n hours.
This means the larger number of sessions to the drive then the longer it
will take to read the tape, meaning the longer it will take to restore.
For this reason it is wise to go for the minimum number of sessions to keep
the drives spinning and to obtain an acceptable restore performance.
This also means that if you don't care about restore then you can set the
maximum number of sessions as you like.

I hope this helps a bit to understand what can drive a networker backup
administrator into insanity.

Bye
Ernie


-----Original Message-----
From: Legato NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU] 
On
Behalf Of William M. Fennell
Sent: Wednesday, October 26, 2005 10:04 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: Re: [Networker] Best usage of tape drives


Our parallelism is at 40.

Three tape devices can take 4 target sessions and the other two can handle two each. Even if we are at 16 streams taking up all of our tape devices, parallelism will

trump the target session limit and keep going up until 40 is reached. So I

should expect to see 40 streams saving right?

--------------------
William M. Fennell
UNIX Administrator
Channing Laboratory



Albert Eddie Contractor AFRPA/ESS wrote:

Archive Performance is kind of an itch to me that I am always trying to scratch.

Speaking to Legato last week we discussed a strategy where I would list various specific directory trees to backup. Then you turn up Parallelism allowing more data streams and voila this results in multiple data streams per drive.

Of course weighing in Backup data drive bandwidth ability, controller bandwidth, LAN bandwidth and then the bandwidth ability of your NetWorker components as well.

(Does anyone else feel like they are tweaking VWs to race in the sand?)

The parallelism setup for the server (default 4 in NW7.1?) means that if you don't have 5 data streams coming in, Networker is only going to use ONE drive and leave the other drive for tape operations.

If you lower your parallelism to 2 you should see the second drive join in when the third data stream is identified. I hope this helps.

Semper Fidelis, /ALE

Eddie Albert, Network Serf
Air Force Real Property Agency
Executive Services/Computer Systems

Desk (703) 696 - 5509 - Hip (703) 517-3855 Eddie.Albert AT afrpa.Pentagon.af DOT mil

-----Original Message-----
From: Legato NetWorker discussion
[mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU] On Behalf Of William M. Fennell
Sent: Tuesday, October 25, 2005 4:41 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: [Networker] Best usage of tape drives

Hi folks,

I have a Server with three tape drives hooked up to it.

I have a dedicated storage node with two tape drives hooked up to it. All drives are in a qualstar TLS-4000 and the tape drives are Sony 700CDX AIT-3. We're running Solaris 8 on the Networker server and 9 on the storage node.

We're at Networker 7.1.

My storage node can of course only write local data to tape.

My issue is that it only uses one drive! So it is trying to write 200+GB nightly from three file systems on this host to one tape. How can I make it use both tape drives? Currently it is taking about 8 hours to backup about 200GB nightly to one drive.

I would like to improve on that performance.

My two ideas are:
1: reduce the number of target streams on each drive to two

and then have one drive take two streams and the other take one stream. 2: Maybe the drives need to be shared with each other?

Many thanks,

Bill

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