REbuilding a VG and want to do it right

[codewallah]

Hi,

I currently have a 6 x 18gb VG with 4 LVs, each of which was originally set up to use 2 disks and then 2 extra copies were made of each LV using the next 2 disk pairs so, hdisk2/3 = 1st copy, hdisk4/5 = 2nd copy and hdisk6/7 = 3rd copy. I want to not use triple mirroring any longer as I need to make better use of the disks and I therefore wish to use 3 disks and have 3 for mirroring. The PPSize is 32mb and each disk has 543 PPs available (max). I need to maximize the space and speed but have read that you cannot stripe and mirror as well. If I need LV1 to have 840 PPs, LV2 to have 480 PPs, LV3 to have 195 PPs and LV4 to have 90 PPs and I want 2 copies of each LV, how would you set out the new VG. My current idea is to use the maximum spread option, place 1/3 of each total PP requirement on hdisk2/3/4 and then either to mirror the VG on 5/6/7 or to create a copy of each LV on 5/6/7. I do not use savevg to backup but find | backup -i..

Your thought / recommendations would be appreciated.

Thanks,
Brian.

 

[unclebrian]

Know of no reason why you cannot stripe and mirror.
I would set up two LVs on hdisk2/3/4 mirrored to hdisk5/6/7 and two LVs on hdisk5/6/7 mirrored to hdisk2/3/4 this will give better performance as AIX reads from the primary copy.

 

[p5wizard]

From AIX 4.2 the primary algorithm is based on disk activity - the least busy disk (based on number of IOs the disks have had to perform in the immediate past) that contains a mirror of the needed datablock will be used on reads.

Before that, it was a very complex/costly algorithm based on the amount of disk territory to cross an a disk to reach a particular block.

There is also an alternate algorithm available since AIX 4.3: round robin, to spread disk reads evenly among all disks.

Primary and secundary mirror do NOT decide which disks will become more heavily loaded.


HTH,

p5wizard

 

[DSMARWAY]

Hi ,
If you run AIX 4.3 or greater you can stripe and mirror , AIX does it PP based striping i.e.

PV1 PV2
hdisk2 - hdisk5
hdisk3 - hdisk6
hdisk4 - hdisk7

So when you create your LV as striped it will place each LP
on a separate disk e.g. 6 LPS

PV1 PV2
hdisk2 hdisk5
hdisk3 hdisk6
hdisk4 hdisk7
hdisk2 hdisk5
hdisk3 hdisk6
hdisk4 hdisk7

Do you have multiple disk trays ?
and are hdisk2,3,4 on separate trays to 5,6,7 ?

 

[costiles]

The way that we do it is thrugh smit. smit lv is the fast path - add a logical volume. After picking the volume group, you will be presented with a screeen where you can select the logical volume name - we let the system name it - the number of logical partitions - the disks to be both in the primary and the mirrored copy of the data - the position on physical volume which we put our primary logical volumes on the outer edge - as this is the fastest - the range of physical volumes should be maximum - this gives you a software striping that in our application is faster than the hardware striping - Number of CopIES - this would be 2 in your case - the primary and the copy. Press return and it creates the logical volume. This will give you a logical volume where the data is spread over all the disks - 1 pp assigned to each disk before moving to the next one - and a mirrored copy where the copy of the pp can reside on any disk other than the primary. We keep the pp size as small as we can on the volume groupbecause our writes are written non-sequentially and that allows more than one write to occur at a time.