AutoRAID performance????

[Jack Fan]

All,
Now I encounter AutoRAID 12H performance issue. My friend bring some suggestion as following :

1.Add-on new disks can improve the disk array performance, but it need to
recreate all lun to make data stripe across 8+4=12 disk.
2.There is no way to estimate the improvement of recreate the luns.

so far, totally db data reach 90% disk space what I can used on AutoRAID 12H (8*18G raw disk, available space 96GB). Could you give me 'different' suggestion?

regards,

Jack Fan

[Bill Hassell]

Unlike simple arrays, the Autoraid adjusts the data arrangement automatically. The fastest performance will be where your data occupies less than 50% of the total disk space. At 90%, you'll get the slowest performance. The only control you have for performance is to use two controllers and alternate the physical channel for alternate links. Or you can double your disk space. Or both.

[Vincent Farrugia · Accepted solution]

Hello,

When the AutoRAID disk array reaches the 90% mark, you will notice a distinct lack of performance. This is for a reason.

AutoRAID technology automatically stores data in either RAID 0/1 or RAID 5. The most used data is typically stored in RAID 0/1 because it is faster than RAID 5, the least used data is typically stored in RAID 5, since it is more efficient than RAID 0/1. These are stored in ratios of 90% RAID 0/1 10% RAID 5.

When you reach the 90% mark, therefore, the AutoRAID is trying to see whether the data is to be stored in RAID 0/1 or RAID 5. It continuously stores data into RAId 0/1, then RAID 5, then RAID 0/1 etc. until it reaches a balance in his opinion. This, of course, is very very slow. You are experiencing this type of thing.

In order to speed up this, you need to increase disk space, as your friend told you. However, he is wrong when he told you that you have to recreate the LUNS to do that. AutoRAID automatically creates the LUNs across all disks.

So, in order to increase a disk, all you have to do is to install the disk in the array, and, if you have Auto Include on and Auto Rebuild on, the array starts to rebuild the LUNs in your array automatically. This can take a long time, like 4 hours or more. In order to increase 4 disks, install them ONE DISK AT A TIME. Let them rebuild before giving it another disk.

50-60% data is the optimum data storage capacity for optimum performance.

HTH,
Vince

[Jack Fan]

Vincent,
Are you agree I do strip LUNs as LV?

[Vincent Farrugia]

Hello,

You don't need to recreate the LUNs, since AutoRAID automatically stripes acroos all disks when LUNs are created.

All you have to do is to add disks ONE AT A TIME and allow rebuild time for all disks.

HTH,
Vince

[Jack Fan]

May I need represent the picture.

Currently status:
First time:
18GB * 8 (physical disk),
15GB * 4 (LUNs),
Create one VG with 4 LUNs,
Create 2 LVs with striping on VG.

Second time:
Create 9GB * 4 (LUNs)
Extend VG.

Third time(on future):
Add 18GB * 4 (physical disk)

Question:
1. Do I need recreate LUN?
2. Do I need do LV creation with striping option on sam?
3. Whether too complex for striping while create LV even have RAID0/RAID1 on AutoRAID internal?

regards,

Jack Fan

[Bill McNAMARA_1]

1. Do I need recreate LUN?

No, there is no requirement.... although, I have heard that internal maps for the LUNs can benefit from this operation.


2. Do I need do LV creation with striping option on sam?
No, the LUN is distributed across all disks in the autoraid. If you stripe your lvol across 2 luns the server has more work to do, but the autoraid has exactly the same.


3. Whether too complex for striping while create LV even have RAID0/RAID1 on AutoRAID internal?

RAID 0 and RAID 1 are not features of the autoraid.. remember it's Auto.. auto between Raid 1/0 and Raid 5.

Later,
Bill

[Jack Fan]

Bill,
Thanks for your suggestion. I got your point.
As your suggestion on item 2.
I think we need to do LUNs re-creation, because of we had striped more 2 LUNs to created LV before.

regards,

Jack Fan

[Bill McNAMARA_1]

The only time to do a LUN recreation is really when you want to increase/decrease the size of the lun.

The lun basically acts like a striped lvol, the only difference being that it has a dsk device file. (and you then use lvm to use it)
The LUN is only used when it is configured in LVM... so if you really want to create an LVOL stripped across more luns, well, yea, create for example 4 LUNs of exactly the same size, and stripe a few LVOLs across them, for all it's worth (even this it really doesn't make that much difference to do so.)

Note that the filesystem and data is completely blind to the lvm organisation, so if you're going to restore from backup, it makes no difference that the lvol is constructed differently to before.

You can really do as you like.

I'm probably way off your point, sorry if I misunderstood!

Later,
Bill