Multi-terabyte filesystem space increase on AIX7.1

Hi,

I need to increase a filesystem from around 1TB to 15TB on a running AIX7.1 TSM server.
This will be by far the largest single filesystem increase I've ever performed, or even heard of.

The volume group already has enough disk available (in fact the filesystem was always intended to be 15TB, it just wasn't initially setup at the right size).

Can I just increase the filesystem to the full required size (chfs -a size=+14000G)?
Would I be advised to do the increase in a number of smaller jumps, say 4 lots of 3TB etc.?

Are there any limits or gotchas I need to be aware of? (The filesystem is jfs2, so in theory it should be able to go to 15TB no problem).

TIA, Alan.

Hello alanp36,

You might need to look at the maximum number of extents allowed for the logical volume. You might need a chlv -x <<large_value_here>> type command.

A few things to think about:-

• What is your PP size for the volume group?
• Can you show us the output for lslv <<lv_name_here>>
• Is your volume group protected? I'm guessing it must be formed from RAID or SAN LUNs, but one should ask :rolleyes:
• Would you be better saying "increase by this amount" or "increase to this amount"?

There should not be a problem going in one go.

Robin

I would suggest to go in smaller chunks - 1 or 2 TB.

Very interesting. Would you care to share with us the reason why? I was under the impression that it would not matter at all.

bakunin

You are right, it would not matter at all, but sometimes I'm very conservative.

If you make it in one step, it takes a long time and if something goes wrong, you have to repeat the whole operation from the very beginning.

If you make it in smaller steps, in case of errors, you repeat just the last small step. If e.g. you don't have enough free space in /tmp, you fail during the first operation. If you wrong calculated the free space in the volume group (you know 14 TB are not always 14 TB you repeat only the last step, decreasing the size of the additional space.

And you can always write in a single line, something like:

# for i in 1 2 3 4 5 6 7 ; do if ! chfs -a size=+2000G /myfs ; then print -u2 f.ck && break ; fi ; done

Thanks for the reply Robin.

By maximum number of extents I assume you mean MAX LPs?

• That is something I will need to increase when I go to do the filesystem increase.

PP size in the VG is 1024GB. It was originally designed for this size filesystem.

Not sure what you mean by is the volume group protected, but yes it is SAN disk.

As regards "increase to" versus "increase by", as far as I'm aware there is no functional difference (assuming one calculates correctly).

Cheers, Alan.

Yes, sorry, extents is more of an Oracle space allocation. :o

The difference in "increase to" and "increase by" determines if you do this:-

chfs -a size=15000G /your_fs

... or this:-

chfs -a size=+15000G /your_fs

The former sets the new size and the latter sets the increase in size, so depending what you start with, there could be quite a difference.

I think you have a good plan and I think that the suggestion from agent.kgb is very sensible. Maybe stop short and do the last 2 extensions yourself. Ensure you don't over-allocate the filesystem. When I last had AIX, reducing a filesystem was not possible - you had to drop & re-create it.

SAN disk is (almost always) provided by protected disk, so probably RAID5 or RAID10 etc., but if you have SAN disk, it is not the concern of the person managing the AIX server, so that makes things easier.

King regards,
Robin

Thanks for the clarifications Robin.

As regards the discussion around whether the increase should be done all at once, or in smaller steps, I note the following:

In the man page for chfs it says

So, it may well be advisable to do the change incrementally in some situations - particularly on live production servers.

Thanks bakunin and agent.kgb for input too :-).

Cheers, Alan.

It's all a far cry from my 1K memory ZX81 with a tape recorder attached ......

zx81 tape - images :o

LOL, that it is.
Still, give it ten years, and we'll all be scoffing at any system with a mere 15TB.

Either that, or the machines will have won.
I, for one, welcome our new robot overlords.

Quick update:

The filesystem increase went very smoothly. I did it in a number of steps, increasing in size as each step completed with no problems or delays.
Smallest increase was 1TB, largest increase was 5TB.

All of them completed very quickly, longest was probably around 20 seconds.

Cheers.