SSA drives - Databse, Mirror or Stripe?

[vb8304]

We have a progress database that resides on ssa drives. 16 drives that are mirrored hence 8 ssavg's. When accessing a database that resides only on ssavg1 only one drive light is showing activity. Would it be better to somehow involve other disks either by using a stripe set or somehting esle? Performance wise is there a better way?

Thanks.

 

[PSD]

wb8304,

Well by the sound of it you have got 16 disks in 1 SSA drawer? and are using 1-1 mirroring 2 disks oposite sides of the drawer therefore you have created 8 VG's. Is that right?

Well 1-1 mirroring will certainly outperform RAID 5 in most cases certainly on writes, but using mirroring and striping ( I think this was introduced in AIX 4.3.2) will provide a large benefit but you will need to re-org. your VG's perhaps down to two VG's 8 disks in each, 4-4 mirroring.

Alternately, my favourite way is with the latest SSA microcode and 4P ssa adapters you can use RAID 1+0, mirroring and striping for databases this really improves performance, in DB2 it improved by up to 40%/...

Does that help?

Any more questions please post

PSD
IBM Certified Specialist - AIX V4.3 Systems Support
IBM Certified Specialist - AIX V4 HACMP

 

[vb8304]

You are correct. That is pretty much the way our setup is. Although we are using a RS/6000 J40 server with MCA, not PCI so the 4P slot would be out of the question unless I am wrong about the meaning of the 4P. We have several databases though. Should they reside on the same VG and keep the system files on the other VG?

I appreciate the help.

 

[PSD]

vb8304,

I always keep rootvg seperate i.e. only the OS to allow quick system restores and backup's. So I agree with the policy.

In you database are you using JFS? if you are I would be inclined to put them into one larger VG and use mirroring and striping over a number of spindles. I would also create > 1 JFS log as this can prove to be contristive to I/O and balance the filesystems over the 2 or greater JFS logs.

1-1 mirroring is the easiest set up you can have but compared to the above you will not be getting the best from SSA adapters and disks.

Hope that helps

PSD
IBM Certified Specialist - AIX V4.3 Systems Support
IBM Certified Specialist - AIX V4 HACMP

 

[vb8304]

So, create a VG that uses 6 out of the 8 drives(since they will be mirrored) then mirror each disk and finally stripe the databases and leave the remaining space for rootvg?

I really enjoy working with AIX but I have to admit I am still getting used to the methods AIX uses even after taking the Sys Admin class. When I create these new VG's I know how to set them up using Mirroring but how do you setup striping? Is it done with the LV spanning multiple PV's?

Thanks Again.
Vince.

 

[PSD]

vb8304,

Yes, that is what I would do. 6-6. You spread the LV over spindles as you have already stated and set up a stripe size 64k is the usual.

If you need instructions on how to set up mirroring and striping then you need to download the redbook entitled:

AIX LVM A-Z introduction and concepts

SG24-5432-00

Chapters 2 & 3 cover striping and mirroring and explain step by step. The redbook really is very good.

Hope that helps

Cheers



Just use the last two disks for rootvg and use mirrorvg to mirror. PSD
IBM Certified Specialist - AIX V4.3 Systems Support
IBM Certified Specialist - AIX V4 HACMP

 

[vb8304]

Thanks, the document helped. Our DBA wants to take smaller steps in resolving our dbase issues in terms of their locations on the SSA drives. Would developing LV's on each of the 8 VG's then placing the dbase over those LV's be considered striping and how do you think that will do performance wise?

Again thanks.
Vince.