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AW: Antwort: Re: 2 LTO-Drives Load-Balancing

2004-03-03 10:06:04
Subject: AW: Antwort: Re: 2 LTO-Drives Load-Balancing
From: Salak Juraj <j.salak AT ASAMER DOT AT>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Wed, 3 Mar 2004 16:09:59 +0100
Hello Patrick,

as far as I know TSM maintaines single I/O queues for each volume.
That said, with 2 migration processes running concurrently
you will have up to 2 I/O on tapes at one time (one per drive),
thus allowing for maximal throughput - if the rest of the system
allows :-)

As for how it it is good for you, further mus be considerated:
Certain LTO drives allow slowed-don streaming mode.
I heard rumours in case of HP it is reached by writing additional zero´s
or tape spacing to tape (and ignoring it when reading),
while some other drives should be really able to slow down the
tape movement. Consult your manufacturer.

How much can oyur Disks deliver:
apart from the fact you have apparently stolen 
that random access device from a museum :))),
there is a question: 20 MB per second per what?
Per Disk spindle - and you have got more spindles?
If yes, you won. 
Split your disk storage pool
into more volumes, one per each disk spindle.
As TSM maintaines one I/O per volume
you will have often 2 I/Os on 2 disks in paralell,
one per spindle, thus almost doubling your overall disk
transfer speed.
But if the 20 MB/s is the speed of your
scsi controller, or of your (single) raid array,
than you have got either an investment or a performance problem.


Another point: if you have got many of small files,
your overall disk transfer speed will fall down even further,
as TSM has to group small files first before sending a packet
to tape. This involves databes seraches and disk head repositioning
in your disk storage pools.
In such case, access speed to DB and transfer speed 
of Log can be very important as well.
And amount of RAM.

regards
juraj






-----Ursprüngliche Nachricht-----
Von: Patrick Rainer [mailto:Patrick.Rainer AT ARZ.CO DOT AT]
Gesendet: Mittwoch, 03. März 2004 15:36
An: ADSM-L AT VM.MARIST DOT EDU
Betreff: Antwort: Re: 2 LTO-Drives Load-Balancing


Hello again

Sorry. Maybe my question can be wrong interpreted.
For example:

I have two migration processes from disk stgpool to tape drive.
My diskdrives offer about 20MB/s.
The question:
Is the transferrate of the diskdrives split up for the tape drives to 50%
for each drive? (10MB/s per drive) (Also means 50% per process)
Or uses one drive the full transferrate which is possible for one drive
(15MB/s) and the other drive only gets the rest (5MB/s)?

My problem -> 5MB/s means permanent Stop-and-Go-mode for one drive.
I would like to hear, that the TSM-server splits up the transferrate. This
means each migration process/job uses 10MB/s.

Thank you.

Best regards

Patrick



Karel Bos <Karel.Bos AT NUON DOT COM>
Gesendet von: "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>

03.03.2004 15:04
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Re: 2 LTO-Drives Load-Balancing






TSM is not load-balancing on a drive level. TSM will use multiple drives
on
a job level.

Regards,

Karel

-----Oorspronkelijk bericht-----
Van: Patrick Rainer [mailto:Patrick.Rainer AT ARZ.CO DOT AT]
Verzonden: woensdag 3 maart 2004 14:41
Aan: ADSM-L AT VM.MARIST DOT EDU
Onderwerp: 2 LTO-Drives Load-Balancing


Hello TSM users, a.a.o.o


I searched the mailinglist archive and the discussion forum, but did not
found a solution for my problem.
We are using TSM 5.2.2.1 for library evaluation. We are testing a HP
MSL5030 with two LTO1 drives.
Our disks provide a datarate of about 20MB/s.
LTO1 supports a datarate of maximum 15MB/s and starts STOP-and-GO-Mode at
about 7MB/s.
My question:
Is the TSM-Server balancing the load of the two drives?
That means: Every drive gets about 10MB/s
Or gets one drive 15 MB/s and the other only 5 MB/s?

We tried to analyze this load, but it isn't that simple. The only way is
to calculate the load out of the transfered bytes and the needed time.
How is it possible to monitor the load of one drive?
(HP told us, we shoud check if the LED's are blinking slow or fast ?!?)

Any ideas??


Best regards

Patrick

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