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Lvol help

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Paula J Frazer-Campbell
Honored Contributor

Lvol help

Hi to all,

I am planning to set up a new triple mirrored lvol on 8 disks and would appreciate some guidance / assistance.

I wish to present as many spindles to this lvol as possible as it will carry a busy database.

As the read/write bias is very much read based then striping will be detrimental, so a plain triple mirror spread across the disks is what I believe to be best.

If you have a more efficient solution to this please say so, also I would appreciate help on laying the lvol and mirrors on the disks in this way.

Thanks in advance.
If you can spell SysAdmin then you is one - anon
14 REPLIES
James R. Ferguson
Acclaimed Contributor
Solution

Re: Lvol help

Hi Paula:

I'd mirror only once. I'd spread the logical volume among the four physical volumes using distributed extents, and then simply create its mirror on the remaining four physical volumes. You end up with a simple physical volume group arrangement to which the subsequent addition of new physical volumes to the volume group is easy to handle. As always, allocate primary and alternate links split between controllers.

Regards!

...JRF...
Paula J Frazer-Campbell
Honored Contributor

Re: Lvol help

Thanks James,

I pull a mirror off during business hours as part of the DR solution and feel far more secure running on a remaining double that a single mirror.

Paula
If you can spell SysAdmin then you is one - anon
John Palmer
Honored Contributor

Re: Lvol help

Hi Paula,

Can't you get a ninth disk and then simply mirror across three sets of three disks?

I agree with James about the extent based striping and controller splitting.

Why do you think that striping will be detrimental to performance? The third mirror should increase read performance.

What database files are you planning to place in the volume?

Regards,
John
Paula J Frazer-Campbell
Honored Contributor

Re: Lvol help

John

Ninth disk would require another FC10 -(cost).

This is a very read heavy database (Universe based Flight only) with in excess of 650 users (Ip and x25).
The bias is so read heavy that striping will slow it down.


So I therefore wish to place as many spindles as possible to the prime of the mirror, I even considered 4 disks for prime and then a two disk, two disk option for second and third mirror.


Paula



If you can spell SysAdmin then you is one - anon
John Palmer
Honored Contributor

Re: Lvol help

One thing to remember is that the only thing different in the 'prime' mirror is that it's first in the list to do reads from.

HP-UX schedules reads from the least busy copy so you would expect to see the 'primary' as the busiest, then the 'secondary', then the 'tertiary' (if you have one).

How long is the third mirror split for your DR solution? If it's a long time then you could go for a three disk 'primary', ditto 'secondary' and a one or two disk 'tertiary'.

Otherwise you could go for two disks for each copy and use the remaining two for something else.

Regards,
John
Pete Randall
Outstanding Contributor

Re: Lvol help

Paula,

As I've aptly demonstrated several times in some of my "answers", I can be a little slow at math. However, if I understand how to read (and I think I do), the FC10 can hold up to 10 drives. Now comes the tricky math part. I really, really think that 8 is less than 10. So it seems to me that you ought to be able to add a 9th drive. Of course I just might be missing something, too . . .

;^)
Pete

Pete
Paula J Frazer-Campbell
Honored Contributor

Re: Lvol help

Pete

Yes FC10 = 10 disks plus 2 internal

Distribution

2 x internal OS mirrored.

2 x FC10 disks = Database engine and volitile busy dirs - mirrored.


So I am afraid that leaves only 8 disks to play with.

Paula
If you can spell SysAdmin then you is one - anon
Pete Randall
Outstanding Contributor

Re: Lvol help

Paula,

Ahhhh! The missing part. I knew you had to better at math than I.

Pete

Pete
Paula J Frazer-Campbell
Honored Contributor

Re: Lvol help

Pete

Just put 2 and 2 together and of course you get ----------------------------------------------------






Eight


Paula
If you can spell SysAdmin then you is one - anon
Helen French
Honored Contributor

Re: Lvol help

Are all disks are of same or different capacity? I think your plan is like this: first 2 disks as mirror of internal OS disks, next 4 willl be primary mirror disk, then next 2 second mirror disks and the last 2 third mirror disk. Then the last 4 disks should be of larger capacity rt? coz, you are going to mirror 4 primary disks to 2 other disks.
Life is a promise, fulfill it!
James R. Ferguson
Acclaimed Contributor

Re: Lvol help

Hi Paula:

As for the "math" discusssion, well, two and two don't make eight, but two and *three* certainly do: 2^3 ... ;-)

Regards!

...JRF...
Steve Lewis
Honored Contributor

Re: Lvol help

Check the writes on the tables before you jump into a 3 way mirror, especially with only two controllers on an FC.

How about this scheme? :

lvol L1 L2 L3 L4 L5 L6 L7 L8
disk1 3 4 5 6 7 8 9 10
disk2 5 6 7 8 9 10 3 4
disk3 7 8 9 10 3 4 5 6

This will give an even distribution of logical volumes over disks, with each disk being split into 3, a primary, a secondary copy and a tertiary copy.





Steve Lewis
Honored Contributor

Re: Lvol help

Sorry, forgot to say that you could add these lvols as CHUNKS or tablespaces to your database table. I attach a file which is better formatted.
Paula J Frazer-Campbell
Honored Contributor

Re: Lvol help

Steve thanks


Config will be :-

8 Disks

1 Lvol of 20 Gig triple mirrored.


Paula

If you can spell SysAdmin then you is one - anon