HP-UX - Securepath or LVM

[Simon White]

We have an HP-UX server dual fibre connected to a EVA3000 through brocade switches. If we have SecurePath installed what advantages are there in using LVM - do we have to use it at all?
It seems that LVM is just another layer between SecurePath and the filesystem.

We use LVM on our existing system (HP-UX +FC10) but to control the mirroring/striping and for path failover/management.

If the new EVA controls the Raid levels and Securepath manages the path failover what is LVM used for?

[Robert-Jan Goossens]

Hi Simon,

You will need both, securepath will create the luns, lvm is needed for creating the filesystems. Further you will need a product to mirror your filesystems. (veritas or mirror-ux).

Hope this helps,
Robert-Jan

[Devender Khatana]

Hi,

You can define one link as primary and other as alternate for one half of disks & for other half you can use primary of first half as alternate and alternate of first half as primary for these. This provides a sort of load balancing. (Allthough load balancing /failover mode is not supported in LVM)

Another advantage you will get will probably file system resizing if this is not supported at hardware level. (I am not sure)

I think these would be the only advantages you will get in this case as mirroring is allready taken care at hardware level.

HTH,
Devender

[Simon White]

Robert-Jan,

I am able to create a filesystem without using LVM just by mounting it on the device file presented by SecurePath.

[Thayanidhi]

May be you are using entire disk as one file system. In general several file systems are required, It's better to configure VG on the disk device file provided by securepath, and do partition using LVM's LV, then FS over it.

This is the general practice.

If you want avoid LVM(for what?) then you have to create several LUNS on EVA and create individual file systems on each LUN!!

LVM overhead is negligible, so you can safely LVM.

Regds
TT

[Steven E. Protter]

LVM has wonderful tools vgcfgrestore for example to put things back together after a disaster.

I've just used all of those tools to go through one. There is no reason to avoid LVM and many reasons to learn and use it with HP-UX.

SEP

[Simon White]

Thanks for everyones replys. To clarify:

I need to create 4 file systems for the application. If I am correct I can do this 2 ways.

1. Create 4 vdisks(LUNS) on the EVA and mount each of the 4 file systems onto the luns.
2. Create 1 large visdk(LUN)on the EVA and use LVM to create 4 volumes which will then have the 4 file systems mounted on them.

I suppose my 2 questions are still:
Why would I go fo option 2 when option 1 seems less complex?

What else would LVM give me when the Raid operations are handled by the EVA and the multiple path management is (and has to be) managed by SecurePath?

Thanks
Simon

[Steve Lewis]

LVM gives you the following extras:

1. the ability to stripe your logical volume over several LUNS for load balancing across disk devices - IIRC Securepath just balances across controllers. Lots of people use this technique to reduce disk busy% and request queue for hard-hit LUNs.
2. the ability to reduce a volume without deleting data i.e. lvreduce just chops extents off the end whereas I don't know what a LUN size reduce would do.
3. the ability to extend a volume into multiple LUNs
4. with MC/Serviceguard, the only supported way to control exclusive access over shared storage (vgchange -a e). There may now be a supported Veritas equivalent for this.
5. with Oracle RAC, the ability to share/spread your database across multiple machines
6. pre-requisite for Mirrordisk/UX and campus clusters using MC/Serviceguard, mirroring of an entire disk array to a secondary in case of total power failure of your primary site, failure of your entire disk array etc.
7. A means to migrate your old data to new storage devices without down-time, using Mirrordisk/UX.

LVM is another layer, but it contains no buffering, just a mapping of logical to physical storage.

[Dave Wherry]

While it is true that using LVM adds a layer of complexity it also adds great functionality. I would suggest you get a better handle on LVM.
http://www.hp.com/education/courses/h6285s.html

Robert mentioned you would also need a mirroring product. Not necesarily true. How are the LUNs created on the EVA? If you are already doing Raid-1 or Raid-5 on the storage subsystem, you may not need to do mirroring on the host.

[John Payne_2]

Simon,

Just a point of clarification:

If you present 1 large LUN to the system, it sees it as one large disk. When you do that, you can only create 1 large Volume Group. (In LVM) If you create 4 smaller LUNs, you can still create 4 Volume groups in LVM.

I have seen too many problems with RAW disk layout. I should clarify that. When the disk fails, I have seen too many problems...

SecurePath only takes care of your path the your machine. It has no bearing on how you use that disk (LVM vs. Raw) Look into LVM at least to the point that you understand what it is used for. (Previous posts get you well on your way.) Then make your decision as to what you will do.

Hope it helps
John