----- Original Message ----- From: "Chris Thompson" cet1@cus.cam.ac.uk To: chris_good@webtop.com Cc: toasters@mathworks.com Sent: Friday, October 06, 2000 4:54 PM Subject: Re: mixing 18GB and 36GB drives
chris_good@webtop.com writes:
Just don't use the mix of 18 and 36Gb drive in the SAME volume. That is bad. I don't see why you can't have different disk shelves of same drives, ie. a shelf of 18s and another shelf of 36s, attached to an
F720.
We have this config on an F760.
NO, what you must not do is mix disk sizes in a *raid group*. Its fine to mix in a volume as long as they're in different raidgroups. I think the confusion arises as many peoples volumes don't span
raidgroups.
Another thing I would advise against is mixing sizes in a shelf.
Seperating different disc sizes into different RAID groups avoids various sorts of disc space wastage in the short term. But it doesn't alter the fact that if you have a mixture of disc sizes within a volume, you are stuck with that state for as long as the volume exists: you can never expand a data plane to effectively use a larger disc.
What are you people talking about?
If you have a raid group of 18GB drives, and add a 36GB drive, the 36GB drive becomes the new parity drive. The old 18GB parity drive becomes a data drive, giving you 18GB of space. After that, all 36GB drives you add give you the full 36GB of space.
(Caveat: This is how Netapp's RAID 4 works. With other vendors, YMMV.)
Bruce