boot HPUX from SAN disks - good or bad

[A.K.]

Hi All,
I tested successfully booting operating system on N class machine from SAN disks – EMC Symmetrix (using HBA and FC cables – 2GB) instead of the internal disks.
The advantage I see is that I don’t have to worry about failing root disks anymore or mirroring and since my systems are anyway using SAN and NAS for database devices and for other applications, I am dependent on EMC anyway.

Does anyone knows of any known problems or issues for this kind of setup?
How can I check performance?
How can I check stability?

Thanks,
A.K.

[Duncan Edmonstone · Accepted solution]

Plenty of folks do this... some think its a bad thing cos it can be hard to diagnose SAN problems when you actually boot off the SAN, but in practice I've found it no harder than with local disks.

Things to watch for:

Making sure you have your PVlinks and alt boot paths defined ('lvlnboot -v vg00' and 'setboot') - Powerpath isn't going to help you at boot time, so you need to make sure these are set correctly.

Look at sar -d for your boot disks - your average service times need to be consistently under 20ms (ideally under 10ms) and your average queue needs to be under 2 (ideally under 1). If they're not you could have perf issues

Make sure your not paging out significantly. This is bad with local disk, but absolute death on a SAN. Check with vmstat.

Keep a recovery CD/DVD available. If you can't boot from the SAN, you can boot from CD/DVD to diagnose.

HTH

Duncan

[Bill Hassell]

Often overlooked: make sure your computer is smart enough to boot from a SAN. These boxes don't look like simple SCSI disks and there is *NO* HP-UX driver to help. The (small) processor ROMs must be updated (or update-able) to talk to the HBA and SAN disk. Note that a very tiny error on the part of the SAN administrator can render your HP-UX box into nothing more than an expensive room heater. And that mistake is impossible to diagnose from the HP side 'cause there ain't no HP-UX at all.

[Torsten.]

As long as the server is using a supported FC HBA to boot from a supported disk array - why not?
(not all third vendor arrays are supported for boot)

A good point to start:

http://welcome.hp.com/country/us/en/prodserv/storage.html

Some things to consider:
- is the array "strong" enough?
(performance and availability?)
- needs the array downtime?
- what happens if you need downtime?
...

[Steven E. Protter]

Shalom,

BAD.

Simpler technology is best for this.

If you have a problem between your box and the SAN you are done. No diagnostics,no boot missing some logical volumes, you are hosed with no recourse and sometimes no way to prove to the SAN admin there is an issue.

Better to be able to boot local.

Local disk for booting performs as well as SAN disk.

SEP

[Torsten.]

Just to add this: it really depends.

If you have enough internal or external (SCSI) disks, you should use them first.
But if you have a "virtual" system like vPars or Integrity VM you probably need at least 1 chassis for each vPar - better 2 for HA.
If you have some - let's say 5 or 10 vPars running, you need up to 20 disk chassis.
In this case I would really prefer a SAN boot. If you have some redundancy it runs very well.

[VK2COT]

Hello,

Technically, both solutions work well,
if designed and built well.

I have seen good designs and I
have seen bad designs (Solaris, HP-UX,
and Linux).

However, non-technical issues are
often the main driving force in
deciding one way or another.

Several other (not often discussed)
items to consider:

a) Is your company constantly buying
and selling businesses (acqusitions)?
I know of several large companies that specifically reject to use SAN.
It is purely based on their business
decision for growth.

That way, when they decide to split company,
they can do it easily... It is difficult to
split servers when they use the same SAN :)

As we all know, many companies do not
grow by good planning, but through
acquisitions and interesting activities to
attract shareholders.

b) Total cost of disks (SAN versus
internal)... Not only the physical
devices, but TOTAL COST of using them
(electricity, air conditioning,
floor space, insurance, global warming
effects, support skills needed to use them,
and so on and so on).

You do not need an expert to use
and build O/S on an internal disk drive,
but you do need more skillful
teams and people to build and set up
boot disk on SAN...

Remember: it is not the technical staff
who run the IT business :)

VK2COT

[UVK]

Hi A.K

The testing you have done may have given you some good results and it makes sense if you opt for booting form SAN, but its important to consider
"what if I run into some issues with SAN ?"

I agree that you dont have to worry about failing root disks but on the other side of it you will have to worry about simple SAN issue which can effect your performance.

I would say the failure modes will be more if you are using SAN, compared to internal disks.

Cheers

[Rita C Workman]

Well Mr. Hassell gave you the caveats, so I'll just voice preference and say that lots of folks do it....but I prefer to keep my primary and a mirror on the box.
If you want to put boot on the SAN, that's your choice, but I'd make it just another bootable mirror and not the only game in town.

Guess cause when I started here I had a box that a predecessor had put this on the SAN - no dat drive - no Ignite tapes - and when that disk died we had exactly what Bill mentions. A big room heater. Mgmt agreed to make what were nothing more than minor hardware fixes back then (like a dat drive and a couple internal disk) and it took me some really lousy long days to fix it....

Rgrds,
Rita