RE: Removing (unconfigured) disks from RAID-5 array?

Pete,

It's been a long time since I've seen such small disks but would raid
striping really explain the difference between 8 and 17GB drives? That,
and the fact that he only has two 8gb drives makes me suspect it's not
raid striping that causing the difference. Because, as you've noted, you
have to have at least three drives in a raid set, preferably four or more.
Basically, when you do raid striping you lose one drive, spread out over
all the drives doing the striping. For example, on one lpar I have two
parity sets. I combined two screens to show this:
One: Size
Unit Type Mode (M)
14 4327 070 70564
12 4327 070 70564
13 4327 070 70564
10 4327 074 52923
9 4327 074 52923
8 4327 074 52923
7 4327 074 52923
Two
Unit Type Model
2 4328 074 105847
3 4328 074 105847
4 4328 074 105847
5 4328 074 105847
6 4328 070 141129
1 4328 070 141129
17 4328 070 141129
16 4328 070 141129
15 4328 070 141129
18 4328 070 141129
11 4328 070 141129
The 074's contain the raid strip and lose some disk space. And if you add
up the size difference (141129-105847) and multiply that by the number of
074's (4), you get the size of one disk (140gb). Or (70564 - 52923) * (4)
= 70gb.

Yes, a three drive raid set, while supported, is a performance killer. And
that's cross platform (IBM and others). Four or more makes a huge
difference.




Rob Berendt