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Autoraid 12H configuration

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unixdaddy
Trusted Contributor

Autoraid 12H configuration

We have a K370 attached to a Autoraid 12H. The autoraid contains 48GB of disk space. This is configured as 9GB for data redundancy and 4GB for active spare. This leaves 36Gb disk space for actual use, which is all allocated.

Now when I originally built the box I didn't know that much about autoraid, so I configured it into 2 Luns, 1 with the root disk (4GB) and 1 with the application (32GB). Since then I've read that autoraid works better if a logical volume is split over 4 Luns (instead of 1 in the case of my big one). So my first question is should I reconfigure it?

Secondly the used space is 15GBs in the 32GB volume, given that it is running raid 0+1 (stripe/mirror) doesn't it requires another 15GB in order to run at raid 0+1, this takes us to the limit of the logical volume. what happens when it goes over 15Gb in used space, does it switch to raid 5 (slower)?

To add complexity to this situation we are running HP Openmail, this has lots of little files. Could this present configuration (1 big logical volume, raid that's switched to raid 5 and lots of small files) account for slow running?

What is the best configuration of LUNS and do I need to think about adding more disk space or deallocating some disks or reconfiguring?
6 REPLIES
Paul McCleary
Honored Contributor
Solution

Re: Autoraid 12H configuration

Hi,

There is a lot of contention over the best way to setup an AutoRAID - I think the 4 LUN thing may be because their is 4 SE buses. Though this is irelevant really because the AR automatically stripes the LUNs across all 12 disks. An effective performant way of setting it up is if you have 2 controllers and attach with 2 HBAs and require 2 VGs (vg00 & vgapp) then create 4 LUNs of half the total size u require. Each LUN will have 2 paths. Create the VG with alternate paths for 2 the 2 LUNs. e.g. c3t6d0 c2t51

Then vgextend the alternate paths to the LUNs e.g. c2t5d0 c3t6d1.

The create your logical volumes by striping across the LUNs e.g. lvcreate -i 2 -I 64 -L ?? -n lvol1 /dev/vg00. Setup up your filesystems. Perform the same procedure for your second VG.

This method ensures that you utilise both channels for your data giving you maximum throughput of 20MB/S for each path.

The AR uses a working set, which basically ensures the most regularly used files are in the fastest access storage, be it cache or RAID0/1. As you utilise the space more data is migrated to RAID5 to provide increased capacity the default is to ensure a minimum of 10% for RAID0/1. Unallocated space is used for RAID0/1 as free space within your LUNs. However, once you use the space in the LUNs it will not be used for RAID0/1 again even if u delete the data, due to how the data is stored.

You can get more info at www.docs.hp.com

Hope this helps, Paul
Bob Inglis
Trusted Contributor

Re: Autoraid 12H configuration

You do NOT need to reconfigure the array if performance is NOT an issue. If performance IS an issue you will need to reconfigure.

"Rules of Thumb"
1) No swap on the Autoraid - Swap can really tie up an Autoraid controler and swap doesn't need data redundancy. The root/boot doesn't have to be on there either.

2) Leave 10% of the autoraid's capacity unallocated - That increases the size of RAID 10.

3) Configure at least 3 LUN's and use controler x and primary link to half the LUN's and controler y as primary link to the other half. Alt. link for each can be the opposite controler.

4) Use at least 3 physical Volumes (LUN's) in each Volume Group and use LVM to stripe across the PV's. This will ensure load ballancing if step 3 was done correctly.
Plan for the future and tomorrow will take care of itself.
unixdaddy
Trusted Contributor

Re: Autoraid 12H configuration

I'd like to thank you both for your comments so far. Paul i can see what you are describing and it is along the lines that I was thinking. The only thing is that for VG00 i prefer to keep it to one disk. For vgapps I'll split it over at least two Luns and use disks from different controllers as my main disks, striping across the two.

Bob I can see your comments and they really confirm what paul was saying. Can you explain to me just a couple of things:-

1)no swap on Autoraid - our machines have no internal disks - was this a bad move my the suppliers?

2)10% free of autoraid? do you mean the total disk capacity. From 48GB (total) we have 4GB as hot spare and 9GB data redudancy leaving 36GB. When you say 10% do you mean off the top (48gb) or off what's left (36gb)?

Also what happens when the used space of a logical volume hits 50% does it switch from raid 0+1 to raid 5 as it can no longer mirror the data it has (no more space)?

Thanks for the info, I think I'm getting there.
Peter Jansen
Occasional Advisor

Re: Autoraid 12H configuration

Hello,

Another big performancehit can be suffered if the AutoRaid "automatically" sets the "Write Cache" to "Enabled".

Please check if this is true for your AutoRaid (i think the command is . If so, please let me know to supply you with further information on this subject.

Best regards,

Peter Jansen
ITchallenge
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Paul McCleary
Honored Contributor

Re: Autoraid 12H configuration

Hi Darren,

Glad u found the info useful.

)no swap on Autoraid - our machines have no internal disks - was this a bad move my the suppliers?

- What machines have u got? This is not always a problem, but most customers I configure solutions for prefer to boot off internal disks, often mirroring between 2 disks.

2)10% free of autoraid? do you mean the total disk capacity. From 48GB (total) we have 4GB as hot spare and 9GB data redudancy leaving 36GB. When you say 10% do you mean off the top (48gb) or off what's left (36gb)?

- part of the benefits of the AR is that you should be really worrying about disk space to this level of detail. If space is an issue you might want to consider upgrading your disks (there are 10K 18GB available, though u might need to upgrade you fans to use them). If budget is an issue HP Re-marketing might be able to help. It should be 10% of total capacity.

Also what happens when the used space of a logical volume hits 50% does it switch from raid 0+1 to raid 5 as it can no longer mirror the data it has (no more space)?

- the AR doesn't work like this. It has tables which show which PEGs are allocated and which aren't. Those that are not used it can utilise for RAID redundancy.

Some of your data from all of your LUNs will be in RAID5 other data will be in RAID0/1, it depends on how your data usage is evaluated by the algorithyms used by the AR as to where this data is stored.

You cannot really control the allocation of data, which is why some DBs don't like 'Auto' Raid devices. You cannot restrict your VG00 to one disk either, even if you allocate 1x4GB LUN it will still be striped over all 12 disks. So don't be concerned about stripping it over 2 LUNs - as long as u set up the PV links correctly.

If u have the opportunity I would try and move the boot disks to internal disks.

Hope this answers your questions, Paul
unixdaddy
Trusted Contributor

Re: Autoraid 12H configuration

I'd like to thank everyone for their contribution. We were able to reconfigure the autoraid over the weekend.

We took a backup of the server and then deleted the root lun and the application lun. we then recreated the system with 3 Luns - one for root and the other 2 for the application.

We then did a minimal installation of HPUX to the root disk, followed by creating a volume group for the app using the 2 LUNS (using 2 disk devices on different controllers, putting in the alternate links after). We then created our apps logical volume across the 2 disk striping it and recovered the system back from the tape.

It look like by doing this we've halfed the backup time and now we do sar stats we no longer see one disk being hammered at 100% but a more even split across the two controllers. I think the users will be happy.