File System /LV question

[normntwrk]

We have a new 550 with 8 - 76 Gig drives set up to boot from Raid 5 so the whole array is rootvg.

We are moving over data that is on another serverthat has multiple File systems /LV's .

My question: Seeing as it is on Raid 5 and it sees it as one disk anyway is it better from a file management / performance perspective to create one LV /Filesystem and bring over the files or stick with the multiple file systems / LV's ?

We would have set it up as rootvg mirrored on two of the drives and raid 5 for the rest (one as a hot spare)but that would drop the usable disk space from 456 Gb to 380 and we are trying to at least double their disk space(from the old machine).

 

[Mag0007]

2 disks = rootvg
6 disks = uservg

does that sound right?

 

[normntwrk]

yes except one of the 6 disks would be a hot spare.

hdisk0 --
--Mirrored = Rootvg 76 Gig
hdisk1 --

hdisk2 -- Raid5 = uservg 304 Gig
made up 6- 76 Gig disks
lose one to parity
and one to Hot Spare

 

[RodKnowlton]

Pros and cons of one big filesystem for everything:

Pros:
- you don't have the problem of needing to reduce an lv so you can give its space to another lv.
- simpler configuration

Cons:
- if/when you add disks to the system, it'll be much more of a hassle to move only a portion of your data to new disks than if data was in logical volumes.
- (THE BIG CON) it only takes one runaway process eating up disk space to ruin everyone's day.


Bottom line: logical volumes give you more flexibility and safety, even if they all live on the same hdisk. It might make sense to use one big filesystem if you're really tight on space and can't add disk, but even then, only for data that's growth is 100% predictable.

Definitely go with the mirrored rootvg and seperate uservg, though. You'll be glad you did when it's time to upgrade AIX.


Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

 

[needcoffee]

norm,
I agree that you should change your VG design. Here are some other cons of both you should consider.

Current setup (All RAID 5) Cons:

1. No hot spare means you better never loose more than 1 disk at a time or your current system state is gone.

2. Rebuilding rootvg will take a long time when you replace a failed drive and you'll probably need all users out of the system to guarantee no data loss due to file lock issues.

3. You won't be able to fit a mksysb on one tape for backup when your system grows.

Proposed setup Cons (rootvg mirrored and uservg RAID 5):

1. If you only have 1 RAID card you'll experience greater I/O wait issues. Operations on rootvg cost you about double the I/O of uservg.

2. You'll need to back up rootvg and uservg on separate media. mksysb only backs up rootvg.

needcoffee

 

[p5wizard]

Size of mksysb need not be an issue because you can exlude dirs with exclude.rootvg file. Other than that I agree with Rod and Needcoffee.

Gut feeling says keep rootvg small. I did the same setup on an 2104-DU3 a while back. Split backplane, 1 side w. 2 disks for rootvg and other side with raid5 group of 4 disks no spare at that time) for uservg. Need at least 5 disks for raid5 otherwise you might as well just use mirroring.


HTH,

p5wizard