New on SAN

[Co van Berkel]

Hi,
We run on HP-UX 11.00 with MC/SG 11.12 and HP-UX 11.11 (v1) with MC/SG 11.16.
These servers are connected to SC10 and DS2300 scsi disk cabinets now.

Now we are planning to connect to a SAN:
- IBM DS4800 (SAN)
- FC disks
- SATA disks
- Cisco MDS 9216i (switch)
- HP A6795A Fibre Channel PCI XL2 Adapter

HP-UX 11.x servers:
- cluster of 2 x rp5450 L2000 (HP-UX 11.00)
- cluster of 2 x rp4440 (HP-UX 11.11 v1)
- cluster of 1 x rp5450/L2000 (HP-UX 11.00)

I am new to a san, so I have some questions.

In our SC10 disk cabinet the maximum PV size is 73GB.

In LVM the maximum PV size is:
65535 (PE's) x 256MB (PE-size) = 16TB

In LVM the maximum VG size is:
16 TB (Max. PV-size) x 255 (max. PV's) = 4.079,93 TB

- Are those maximum only theoretic?
- Is the maximum LUN size on HP-UX 11.00 and HP_UX 11.11 v1 both 2Tb?
- What should I choose as maximum LUN size?
- What should I choose as maximum PE size?

Is there somewhere a cookbook for me to get better understanding how to configure LVM / LUN s on a SAN running HP-UX 11.x using MC/SG?

Regards,
Co van Berkel.

[IT_2007]

There are LVM restrictions to extend volume group. But do you really need one volume group so big?

Your calculations are correct and can't go beyond that. If you really see the future growth would be more than that then prefer Veritas Volume Manager would be best option instead of LVM.

[Geoff Wild]

For filesystem sizes:

http://docs.hp.com/en/5971-2383/5971-2383.pdf

Your main issue is - HP-UX 11.00 will no longer be supported after Dec 31, 2006 - so if you are truly needing Mission Critical - then you better plan on upgrading those toute suite

As far as migrating to the SAN - it depends on how your existing VG's were created...

If you PE Size is only 8 Mbytes then you won't be able to bring the full 73GB into the existing VG - you will have to create new ones...

I used -s 16 -p 128 to vgcreate recently when adding 72GB LUNS....

Rgds...Geoff

[Co van Berkel]

Hi,

Thanks for your reactions.

IT_2007:
The SAN administrator tellsâ s me that they want to reduce the amount of LUN's by creating only big LUN's.
We don't need bigger LUN's than 1Tb, but I want to know what is commonly used, what is preferred and why.

Geoff Wild:
Thanks for the information about the file systems. Thatâ s something I didnâ t think of yet.

Yes, HP-UX 11.0 should be upgraded so we are also in a process of migrate to new servers. But we have to connect first to the SAN with these servers.

About: â If you PE Size is only 8 Mbytes then you won't be able to bring the full 73GB into the existing VG - you will have to create new ones...â
I think this depends on the Max. PEâ s setting when the VG was created as I am right?
(65.535 (Max. PE's) x 8 Mb (PE-size) = 524.280 Mb = 512 Gb maximum PV-size)

Regards,
CvB

[Wim Rombauts · Accepted solution]

As for LUN creations on SAN with MC/SG :
You need a separate volume group for every package
You can create one big LUN vor the volume group and thus have a volumegroup with - for as far as the OS is concerned - 1 huge disk.
But it would be creasy to create a 2TB LUN if your system only needs some GB's. You cannot create multiple VG's on one big LUN, so oversized LUN's would be a waste of time.
Furthermore, I myself noticed that there is some kind of disk I/O bottleneck if you use one big LUN. If you would create 2 or 4 LUN's, and then a VG with those 4 LUN's and LV's with distribution (-D y), you will notice that HP-UX will parallelize I/O over the 4 LUN's and therefor has a faster I/O then when it has to serialize all I/O to the single LUN.
Therefor, I stopped using one big LUN per VG and I switched to using 2 to 4 LUNs, depending on the IO pressure I expect.

[IT_2007]

IT_2007:
The SAN administrator tellsâ  s me that they want to reduce the amount of LUN's by creating only big LUN's.
We don't need bigger LUN's than 1Tb, but I want to know what is commonly used, what is preferred and why.

Geoff Wild:
Thanks for the information about the file systems. Thatâ  s something I didnâ  t think of yet.

Yes, HP-UX 11.0 should be upgraded so we are also in a process of migrate to new servers. But we have to connect first to the SAN with these servers.

About: â  If you PE Size is only 8 Mbytes then you won't be able to bring the full 73GB into the existing VG - you will have to create new ones...â Â
I think this depends on the Max. PEâ  s setting when the VG was created as I am right?
(65.535 (Max. PE's) x 8 Mb (PE-size) = 524.280 Mb = 512 Gb maximum PV-size)
======================

It is really depends how your systems has been designed for the application like IO, performance or high availabilty etc.. Because you may or may not have lot of disks with stripes, without stripes also.
I have seen max. size of LUN goes upto 1TB and not more than that.
You are correct about max. PEs setting when you create volumegroup.

[Rita C Workman]

The size of your lun depends on the size you NEED to make it...and what you'll be doing with it, that could affect performance.
I run UNIX and SAN and I have luns as small as 8gb and luns up to 400+Gb. I have lvols as big as a 1Tb. Notice I said an lvol at a terabyte not a lun.

It really is a matter of management. Smaller the lun, the more to keep track of. The bigger the lun, the less to document and keep track of.
Providing making them too big doesn't impact performance, then make them larger.

Sounds like your SAN Admin doesn't want to manage alot of luns; hence the stipulation to make the luns larger.

Don't let the issue of managing disks become a threat to your I/O performance.
And don't let being used to smaller luns make you feel like you have change everything now to something bigger than it should be.

....balance....in....everything....

Kindest Regards,
Rita

[Co van Berkel]

Thanks all for your reactions.
It all is helpfull to me to make the right choice.

Regards,
CvB