From: John Gormley (IMCEAEX-_O=SOUTHERN+20CROSS+20UNIVERSITY_OU=SCU-NT_CN=RECIPIENTS_CN=JGORMLEY@sc)
Date: Mon Sep 23 2002 - 02:24:07 EDT
Got some greatly appreciated answers here. Many thanks to :
Blair Phillips
Pat O'Brien
Robert Fridman
Mandell Degerness
Raul Sossa
Alan@nabeth
SUMMARY:
The Jury is out on whether to use LSM or poke at it with a very long stick -
original question and answers are attached to the end of this e-mail.
Information on the kzpac and kzpcc:
The KZPAC doco is at
http://www.compaq.com/alphaserver/products/storage/ra230/index.html
The KZPCC doco is at
http://www.compaq.com/alphaserver/products/storage/kzpcc.html
The KZPCC supercedes the KZPAC, unfortunately the doco for the KZPCC does'nt
include the AS1200 amongst it's list of supported systems, the KZPAC only
supports up to 9Gb drives and logical volumes up to 32Gb.
Single channel or 3 channel? - depends on how many devices I want to add.
Please read the attached replies for some great opinions on this subject.
ORIGINAL QUESTION:
I want to set up raid on two of my systems one a AS1200 the other an ES40,
both on 4.0g. They are both already running raid sets Raid 5 on a RA3000 and
Raid 0+1 on an RA7000 respectively. What I would like to achieve is raid on
the internal disks, Raid 1 on the system disk and raid 5 on data disks (I
gleaned this from the 300 odd archives I have read today). I am about to
purchase a single channel KZPAC-AA for each machine from our vendor, but
during my reading I came across the KZPAC-CA 3 channel card.
Questions:
Can I achieve what I want to do with a single channel card per machine?
Is there some good online doco I can find on the digital/compaq/hp sites?
Do I really have to use LSM or will hardware raid do the job?
REPLIES:
BLAIR PHILLIPS:
Hi John,
I'd stay away away from the KZPAC if at possible. They don't do a very good
job of recovering after any problems, and tend to mark RAID sets as having
problems when they are really quite OK. You can usually just tell the
controller that the RAID set is really OK, but it always leaves me with an
uneasy feeling.
The other problem is that the KZPAC has a maximum logical volume size of
32G, and a maximum of 8 logical volumes. This makes it hard to use recent
drives larger than 9GB.
Personally, I'd rather use 2 SCSI buses and LSM provided RAID 1+0. Much
better performance.
The KZPCC is a better controller in all respects, but it isn't supported on
the AS 1200, AFAIK.
In either case, I'd buy the 3 channel controller rather than the 1 channel.
There isn't much difference in price, and the 3 channel gives you more
flexibility for the future, even if you only use 1 channel in the short
term.
In response to your questions:
> Can I achieve what I want to do with a single channel card
> per machine?
Yes, with some loss of performance and reliability. I like to split mirror
sets across separate SCSI busses for performance and to ensure that a SCSI
problem only affecs 1 copy. If possible RAID sets should have 1 member per
SCSI channel, but that is not really proactical with only 3 channels.
> Is there some good online doco I can find on the
> digital/compaq/hp sites?
The KZPAC doco is at
http://www.compaq.com/alphaserver/products/storage/ra230/index.html
The KZPCC doco is at
http://www.compaq.com/alphaserver/products/storage/kzpcc.html
> Do I really have to use LSM or will hardware raid do the job?
I have set up systems purely with KZPCCs or HSZ80s and not used LSM at all.
The advantage of LSM is that you can mirror across totally independent
hardware systems and avoid a single hardware point of failure.
(Of course LSM is still a single point of failure, and may represent a
greater risk that the RAID controller, given the complexity of the recovery
process and the scope for human error in that process.)
****************************************************************************
**************
RAUL SOSSA:
Questions:
Can I achieve what I want to do with a single channel card per machine?
>>> AlphaServer ES40 uses a BA610-6D and current DS-KZPCC-CA supports it.
>>> Just review that your ES40 has this internal drive cage (just one, not
two).
>>> If you have two internal BA610-6D drive cages in your ES40, you will
need
>>> two DS-KZPCC-CE on channel controllers or one DS-KZPCC-CE three channel
controller.
>>> The AlphaServer 1200 does not appear as supported by the KZPCC
controller.
>>> Only the DS20E and AlphaServer 800, the're similar servers but not the
same.
Is there some good online doco I can find on the digital/compaq/hp sites?
>>> http://www.compaq.com/alphaserver/products/storage/kzpcc_ac.html
Do I really have to use LSM or will hardware raid do the job?
>>> Avoid LSM, you can get it by the hardware RAID.
>>> Always use hardware RAID, it has been always better than software RAID.
****************************************************************************
************
MANDELL DEGERNESS:
The answer is going to depend on how many disks you have internally and
whether or not you intend to connect an external storage works enclosure to
the KZPAC-CA. If you only have 5 to 7 disks internally and no intention of
adding more, the KZPAC-AA will probably do all you need to.
****************************************************************************
***********
ALAN@NABETH:
You can use LSM, hardware RAID or both if you want. It really
depends on what kind of availability and performance you need.
The advantage of a hardware array controller (of nearly any
sort) is that it offloads the RAID work to the controller.
To the host, whatever logical units it presents, just look
like a bigger more available disk (using an appropriate RAID
level). The disadvantage is that the RAID subsystem is itself
a single point of failure and limits the performance to that
of the one host interface.
Using LSM you can mirror or stripe across two or more such
subsystems allowing for better availability and performance.
The value of the 3 channel KZPAC over the one channel is
that the load gets distributed over three separate SCSI
busses. A given SCSI bus can only have one data transfer
going at a time. In a single bus adapter, this can limit
the performance in many work-loads. The three channel
adapter also allows for connecting more devices.
****************************************************************************
***********
ROBERT FRIDMAN:
I have a DS20 and DS10 both with the 3 channel KZPCC. What you want
to do will work if you have the right internal disk cage (I don't
think all will work with the KZPCC). I had the exact configuration
you want in an ES40.
I'm not a great fan of the KZPCC. It needs a video card to configure
(there is a CLI, but I found it buggy, and had to get a generic video
card). RAID sets take a huge time to build, but apparently you can
use the RAID set before the build it fully complete.
Make sure your firmware will support the KZPCC.
****************************************************************************
************
PAT O'BRIEN:
I think the answer is in your budget and your desires. Truly redundant roor
disk will be on 2 disks in separate ba boxes connected to different host bus
adapters and kept in sync, and ideally with one off site. However this is
not always practical or desired. I am biased against the 1 or the 3 channel
raid controllers, even though I have extensive experience. Maintenance
requires down time to replace disk, and depending on configuration, you may
need to delete logical disks, before recreating disks( raid0 which need
deleteion and recreation after failure). Then there is the max logical drive
size 32gb. I think minimally 2 disks in the same ba350 provides a good
level of redundancy, and if you split the ba shelf and use 2 host bus
adapters even better utilizing lsm to mirror( synchronize) is fine. LSM can
not be user friendly, but with a little experience is not that bad. One of
those things that when it works, you don't know anything about it till it
breaks. And then their is the shelf life of the raid controller. many
models have already been retired, with more to come.
and a further note from PAT OBRIEN
To me the choice to use the swxcr( aka 1 or 3 channel raid) controller or
lsm is a no brainer. use lsm.. Yes it does get persnickity, but it really
is a great tool. Back in the 3.2 osf days it was worse, and in 40f just
about flawless, and in 5.1 even better. Install in 5.1 has also been
simplified. I have 6 huge lsm systems averaging 4-6 tb under lsm controll
comprimising 300 lsm volumes apiece. Just when I think their isnt anything
new, comes a surprise. Then theier is the cost. kzpba will be cheaper than
the swxcr's, or just another drive if that is all that is in the budget.
Regards, John
John Gormley
Senior Unix Systems Administrator
Information Technology and Telecommunications Services
Southern Cross University
LISMORE NSW
AUSTRALIA.
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