EMC meta-volumes vs extend based striping

[BradF]

Greetings,

We are running SAP on Oracle on an EMC frame.

Currently we are using extent based striping across 6 hypers using PV links. We are seeing good performance with this. We are not using powerpath.

We are talking to EMC about a new frame and they are recommending using meta-volumes with 4 disks with 128k stripe size and powerpath. This would stripe the data internally on the EMC and present a Big pre-striped disk.

We are also using ServiceGuard for our Production SAP database.

What have people seen as better?
We would be going from striping across 6 disks to striping across 4.

What we have works now and I am concerned with the powerpath overhead and added complexity.

Thanks,

-Brad

[harry d brown jr]

Brad,

The funny thing is that we all get "mixed" messages from EMC. I've personally have seen different performance results using hp-striping, extent-based-striping, and no striping without any consistency. I'm not sure there is any clear answer, but I'd sure like to hear other people's comments!

live free or die
harry

[Roger Baptiste]

Hi,

<>

I use MetaVolumes on two systems. They rock! (so far at least). I moved the database from a regular volume
EMC to the one configured with MetaVolumes and the performance seems much better on the Metavolumes one.
So, i would suggest to definitely go for the Metavolumes. The good thing
about it is, you spread the load on all the disk adapters
using the Metavolumes. On top
of it, when you use the distributed striping at the LV level, you would using bunch of meta's to divide the load even further.
We use 36Gb disks, which are
split into 9 chunks. Then, one chunk of 8 disks are grouped together as a Meta giving it a Size of 32Gb. This is what you will see on the system as a physical lun.

Then, we take four of these
metas (4*32) and group them in a VG = 128 Gb (approx 120Gb usage), using distributed striping of 2MB PE extent. (128Kb is too much of a overkill, IMO).




Meta!



4 Metas per disk is good.

<>

I am not using Powerpath.
I actually tested it before
going into production. Found it flaky (i know there are differing opinions on this one), so jettisoned it.
I would prefer to have control over the PV links, rather than give up the control over it , unless the product is reliable.

Put enough thought on configuring the metas. lay the VG''s out neatly. (use the coloured MAP which the EMC engineer gives out to ease this process). Get the DBA involved after creating the VG's, such that he knows how to spread his stuff on the VG's.

HTH
raj

[BradF]

With PV links and extent based striping IO is spread across the Fibre connections to the EMC unit. We have 2 connections to the EMC from each host.

With meta-volumes all access to the meta-volume (presented as one disk) will go through one Fibre connection. The alternate link will not be used except in case of failover.

Powerpath would spread the IO to both the primary and alternate link.

What kind of issues did you have with powerpath?

Did you compare metas vs extent based striping?

[Deshpande Prashant]

HI
We are using power path here with EMC frames.
Some of my hosts even have 6 fiber connections to EMC frames. I found it much easier to maintain with poerpath,as I do not need to bother about the PV and VG combination to use.
With power path you also have option of grouping the links, defining all/some links to particular VG.

One more advantage with Meta volumes being, it will reduce the total number of disks per fiber channel.

Thanks.
Prashant.

[Roger Baptiste · Accepted solution]

<>

Yes it is. Meta adds one more level of striping (at the EMC level - across EMC disks) to this.

<>

I think it is better to use
both the PV links. in vgcreat specify pv''s as
primary alternate alternate primary ...
Ofcourse this does not apply, if you are using powerpath since PP takes care of the load balancing.

<>

Yes.

<>

It takes full control of the pvlinking and runs at kernel level, which means you cannot disable powerpath when the system is running. Even that was ok with me, until
i ran into an issue trying to disable powerpath. I tried disabling it by shutting off the startuup script and rebooting the system. When the system rebooted, powerpath daemon was still running! Then, i found that it is because the kernel contains Powerpath related changes and that needs to be backed out too. In the meanwhile, some VG's couldn''t be accessed.
I didn't get clear answers from EMC support, so dropped the ball and went the manual route.

Except for this, Powerpath worked fine during the tests, splitting the load seamlessly.



Yes. Metas scored over the regular lun striping. Actually, even in Metas i use
Extent based striping (that is
VG distributed extents - PE size 2mb ; -D y -s g option in lvcreate).
If you want to run disk tests with different pe extent and striping configuration,use a disk tool
iotest available from www.soliddata.com .

HTH
raj

[fg_1]

Brad

We have multiple frames here and in each type of setup (lawson/Data Warehouse/Caremanager) we have meta volumes and powerpath working in tandem.

The powerpath is excellent since it has provided load balencing across fibre connections so that no one chain is bombarded with I/O.

As for the performance on the frame, the larger frame that they are proposing to you will probably come with faster drives (RPM) and a larger cache, this will more than make up for going from extent based 6 disk to meta-volumes with 4 disk. I am quite sure that you will benefit from this.

Good luck.

[Jason VanDerMark]

Brad,

As has already been stated by others, the meta-volume route is definitely the way to go. One of the greatest things about meta-volumes is that not only are the hypers that make up the MV on different disk channels, but their mirrors are spread throughout the disk channels as well. What this does for you is that within the Symm, when a write, for example goes to cache, the Symm checks both paths, the one to the primary and to its mirror. It will choose which one has the least load and then sync the other after the fact. This work all happens on the Symm side with no interaction from the host. As you can probably realize the Symm takes all of the load for handling the striping/mirroring of your data. This can free up a good number of cpu cycles on your host as compared to extent based striping which is all on the host. You get the best of both worlds by using Meta-Volumes. I hope this helps.

Regards,
Jason V.

[Steve Miller_4]

metavolumes+powerpath=fast&easy

Just don't forget to add the alternate links to the volume group in case you have a controller failure.

Also, don't go with a metasize over 35-40GB. Eight 8.5GB slices fit nicely on 73GB drives and give you a ~35GB disk. I make each disk it's own LV for easier management, but that's personal preference.

Regards,
Steve