striping on EVA8100 with LVM

[dmsmith32]

Hello

I would be grateful for any advise on the following.

I am unsure whether I should be striping my logical volume or not. The setup will be :

10* 1TB luns (Raid 5) presented from an EVA8100 (disks are all in the same disk group)

I need to create 1* 10TB filesystem. Should I stripe this within LVM or does the EVA8100 handle this sort of function for me because of the way it spreads data across the disks. NOTE: I dont want to use Raid 1 on the array, needs to be Raid 5

Would striping from LVM just disrupt the way the EVA8100 works?

At first I thought striping with LVM would be good, but I have since read that striping on arrays is not always the best idea. Is this correct?

Any help givem will be much appreciated. Please ask questions if you need more info.

regards

Darren.

[Ganesan R]

Hi,

First, Why do you want to striping the disk which is already RAID5 striped at storage and which is unusual?

Answer for your question is yes. You can stripe at LVM level. Because lvm doesn't what kind of striping or whatever done at storage level on the LUNS. For LVM it is just a disk.

You can do both block level striping and extend based striping.

But personally I feel it is going to be waste of space.

[Ganesan R]

Hi,

Typo on my last post. You can ignore the last line "I feel it is going to be waste of space" .

We are not going to loose any space by any means.

Just to add few things along with my previous post.

Mirroring will not work with block level striping. Hope you won't require mirroring on storage LUNs(Since it is raid5)
=>Use -i(stripes) -I(Stripe size) along with lvcreate command for block level striping

For extend based striping you need to have PVG(Physical volume group)

Use -D(Distributed) -s g (use PVG) along with lvcreate command for extend based striping.

[dmsmith32]

Hi

Thanks for your reply.

Re: why do I want to stripe the disk which is already RAID5 striped at storage?

That is my question really. Do I need to? Is there any performance benifit striping the Logical Volume over the 10 (Raid 5) luns or should I just concat the disks into one large Logical volume.

Is striping necessery at all?

regards

[Ganesan R]

Ofcourse. You will get the best performance. Because from LVM perspective, it's going to write and read the data from different disks rather than single disk in case of non-striping. It is upto the storage overhead how it deals with LUNS.

But the question here is, we do not know how the LUNS are already striped using RAID5. We are striping over already striped disks.

[dmsmith32]

"But the question here is, we do not know how the LUNS are already striped using RAID5. We are striping over already striped disks."

And this is the question that prompted my doubt. I think the EVA does do some striping of the raid 5 data in the RSS (Redundant Storage Set) that the disks are located in. I just dont know enough about how this works, which is why I am here :o)

[Hein van den Heuvel · Accepted solution]

>> Is striping necessery at all?

You did not mention an OS version / platform, nor the HBA/switch setup.

Striping will make it easier to ensure that all HBA's are used in a balanced fashion.

I would go extend striping with large extends. The EVA will already be doing fine grained striping (raid-5) over the physical drives. All the extend based striping will add is a potential round-robbing over the adapters (depending on preferred/dynamic path availabilities).

Considering that all the units will have access to all the the disk already, you may want to review to need to combine them in the first place.
Yeah I know, it is 'simple' to have just one place to look, and there will be no need to space balance, but 10TB is a whopping big mount point to make a backup from, to search, or to recover from a software or operational ooops.
Maybe use a few (less than 10, not dozens) visible volumes/drives of somewhat tailored size (give or take 100GB :-) and have some spare space to add to specific volumes which prove to need more?

hth,
Hein van den Heuvel
HvdH Performance Consulting.

[dmsmith32]

Hi

#model
ia64 hp server rx7640
#uname -a
HP-UX sn4730c B.11.31 U ia64 0989426312 unlimited-user license

4* 1GB HBAs connected to HP StorageWorks 4/32B SAN Switch (4100 brocade)

Because it is HPUX 11.31 I will be using the Agile addressing (persistant addressing, so I believe this should help with the preferred/dynamic path availabilities

The filesystems will not be backed up, so this is not an issue.

[dmsmith32]

should have been 4* 4Gbit HBAs

[Ricardo Rocha]

Hi

As you are using HP-UX 11.31, the new I/O stack will allow to use load-balancing across the HBA's. In this case, I feel that stripping will no be necessary.

We found it useful on older flavours as 11.11 or 11.23 without EVA SecurePath, where we used simply PV-Links.

In your case, you can keep it simple!

Regards,

Ricardo

[sujit kumar singh]

Hi

Just to point out more one thing, If you create a Stripped LV with 10 Columns (disks )understand that when you are going to add disks and extend the LV you shall be requiring 10 cols that is ten LUNS to do so.Or for the extension of such an already ctreated LV by 2 Disks you shall have to Change the Policy non-distributed.


Sorry if that has been mentioned earlier.
regards
sujit

[Emil Velez]

Depends. If you were going to stripe over 5 luns presented to the same controller then striping will probably not help you since the I/Os will go through the same controller. So I would not recommend striping.

I would suggest you first create the luns as simple as possible and only stripe across controllers if you have a bottleneck at the controller level.



If you will be striping across 5 luns and each of these 5 luns are presented to 3 different controllers and you alternate the primary path you can use striping to spread the I/Os to different controllers

There are a couple of issues

1. 11.31 does load balancing across all paths on its own if you use the agile device files.
2. if you use VXVM instead of LVM it can do load blancing and you can convert your volumes from non-striped to striped at will.

good luck.

[dmsmith32]

Thanks for all the replies. I am going to set one of each up and do a bit of testing.