cx3 - cx system disks

True

Are you talking about the disks needed for a Clariion ?
The first 5 disks (0_0_0 to 0_0_4) contain the Flare code and the vault area and there's nothing you can do about this. Of those first 5 drives not all space is used, but you will see that less space is available on those 5 disks compared to 5 identical disks in for example positions 5 to 9 (set up to the same RAID level of course).
AFAIK on older Clariions with Flare 19 the space used for Flare and vault is 6GB per drive and with higher Flare codes (all CX3 models) this is 33GB per drive.

Example: on flare 19 and the first 5 drives being 146GB drives (133GiB) only 100GiB remains per drive, so in RAID5 (4+1) this is 400GiB (4 x 100).
On Flare 26 and the first 5 drives being 300GB drives (273GiB) only 240GiB remains per drive, so in RAID5 (4+1) this is 940GiB (4 x 240).

One last thing: 1GB = 1.000.000.000 bytes (10^9), while 1GiB = 1.073.741.824 bytes (2^30).

Message was edited by:
RRR

So to answer your question: you need at least 5 drives.

note - if you do use the available space from the first 5 disks for host I/O, make sure you don't overrun the disk I/O capacity as it will have significant negative effect on the SP's performance.