AutoRaid hot swap question?

[John Love_3]

This is a two part question. The first question is very stupid, but I'm just checking.

1. can you hot-swap disks?
2. If I replace a 9.1GB disk with a 36GB disk, is the difference wasted, or does it make the difference available?
Does this make sense?

Thanks,
John

[A. Clay Stephenson]

Hi John,
Not stupid at all. Yes you can hot-swap.
You need to make sure that Auto Include is enabled on the front panel. Then remove the 9.1GB and install the 36GB and walk away. Lots of lights will flash and after a while 'Ready' will be displayed. At that point you can replace a 2nd disk.

The answer to the second part of your question is no - you will get almost no benefit from one 36GB drive; you need at least one more. 4 would be better still. The AutoRAID has to reserve enough space for failure of the biggest drive. With one 36GB in the box guess which one is the biggest?

Regards, Clay.

[James R. Ferguson · Accepted solution]

Hi John:

1. Yes, some disks are indeed "hot-swap-able".

2. Replacing a 9GB with a 36GB disk may or may not lead to "waste". The number of physical extents that can be allocated on a physical disk is controlled by the 'max_pe' parameter to 'vgcreate' and cannot be changed once set. The default value is 1016. If the size of any physical volume exceeds 1016 times the 'pe_size', then the default value for 'max_pe' is adjusted to match the physical
volume size. Unless adjusted at 'vgcreate' the 'pe_size' default is <4> MB.

Thus, it depends upon how the volume group was established as to whether the additon / replacement of smaller by larger size physical disks will truly result in their use, or will result in "waste".

...JRF...

[John Love_3]

Well, that's an ear full.
Thank both of you.
Clay, there are 4 other 36gb drives and 8 9.1GB drives. I was just thinking that I should have replaced one of the 9's with the 36 when I added the other 4 36's and reconfigured all the LUN's. Dumb, but was hoping to recover from my stupidity.

I was hoping to use the difference as device swap. James, does that make a difference with the max_pv values, etc.?

John