Hi Gerald,
I think that the answer to your question really depends on how your disk
subsystem works and spreads volumes through the RAID arrays. the object of
the game is always the same: spreading data as much as possible on all
disks in the subsystem and try to parallelize everything. in my experience,
with intelligent disk subsystems such as the IBM shark or similar, you
would want to fill the machine with lots of small (say 10GB) volumes. not
as much because things would change so much in the RAID rank, but to have
all device adapters (they would be Fiber Channel adapters on the Hitachi
machine and SSA adapters on IBM's for example) work, so as to use as much
of the global bandwidth of the machine as possible. the end result is a
very nice sight of hundreds of little LEDs flashing to indicate disk
activity throughout the machine. heartwarming...
ok?
Cordiali saluti
Gianluca Mariani
Tech Support SSD
Via Sciangai 53, Roma
phones : +39(0)659664598
+393351270554 (mobile)
[EMAIL PROTECTED]
Gerald Wichmann
<gwichman@ZANTAZ. To: [EMAIL PROTECTED]
COM> cc:
Sent by: "ADSM: Subject: Re: allocating disk volumes
on RAID5 array
Dist Stor
Manager"
<[EMAIL PROTECTED]
.EDU>
28-05-02 23.01
Please respond to
"ADSM: Dist Stor
Manager"
Yes I'm well aware of the different pro's and con's to using various levels
of RAID vs non-RAID. In my application protection is paramount and
mirroring
is simply too wasteful to use. I've used RAID5 repeatedly in the past in
regards to TSM and have always been very happy with the results. So the
issue here isn't really what to use or not but rather whether there's any
pro's or con's on the way you go about creating volumes on a RAID5 array.
E.g. lots of smaller volumes or fewer large volumes? Having lots of RAID5
arrays as was also suggested isn't really practical because these days it's
rare you don't have fairly large disks (18 or 36GB each) so in that example
of 100GB you're really only talking 1 RAID5 array of 4-5 disks.
Bottom line is I was just speculating out loud perhaps on whether there
were
any pro's or con's to how many volumes and what size one would make the
volumes on a RAID5 array. Say you had a 100GB RAID5 array. Would you create
10 10GB volumes or 2 50GB volumes? Does it matter since it's all just going
into a big array?
Regards,
Gerald Wichmann
Senior Systems Development Engineer
Zantaz, Inc.
925.598.3099 (w)
-----Original Message-----
From: Gianluca Perilli [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, May 28, 2002 1:35 PM
To: [EMAIL PROTECTED]
Subject: Re: allocating disk volumes on RAID5 array
Hi Gerald,
I think you have to consider that if you use RAID5 logical drives, you have
to calculate and write a parity every time you write any data on the disk:
so if you have a write intensive application, RAID5 is not so efficient as
other RAID protections (1,10, etc); if you have instead read-intensive
applications RAID 5 is a good choice because it gives you the possibility
to use more physical drives concurrently.
Furthermore RAID 5 is the most efficient protection regarding the optimal
usage of the available phisical capacity, and it is more and more efficient
as the number of physical drives in the array increase; but at the same
time as the number of physical drives increase, the performance goes down
(because you have to calculate the parity on a larger number of blocks):
probably the best compromise is a number of 7/8 disk drives/array.
I hope this helps.
Cordiali saluti / Best regards
Gianluca Perilli
Gianluca Perilli
Tivoli Customer Support
Via Sciangai n° 53 - 00144 Roma (Italy)
Tel. 06/5966 - 4581
Cell. 335/7840985
Gerald Wichmann
<gwichman@ZANTAZ. To:
[EMAIL PROTECTED]
COM> cc:
Sent by: "ADSM: Subject: allocating disk
volumes on RAID5 array
Dist Stor
Manager"
<[EMAIL PROTECTED]
.EDU>
28-05-02 21.14
Please respond to
"ADSM: Dist Stor
Manager"
Since a RAID-5 array shows up as one big filesystem, what's the best
strategy for determining how many and of what size disk pool volumes to
create for your primary disk storage pool? For the most part I don't think
it really matters unlike allocating volumes on individual disks but perhaps
I'm not considering something.
Thanks..
