What is the useable capacity on RAID 5 (7+1)?

[RMT1]

Hi,

For a Vmax, we are defining a mainframe environment on 400GB FC HDAs, with a RAID 5 (7+1) configuration. Being allotted eight array groups or 64 HDAs, I am told that I can expect to have 21.51 TBs of useable space to configure. It was explained like this to me.

Each 400 GB HDA formatted as a CKD device yields approximately 382 GBs of useable space. With 64 HDAs, my raw capacity is 64 * 382 GBs or 24448 GBs. The useable RAID 5 capacity is 88% of the raw capacity or 21514 GBs (24448 * .88). The parity for RAID 5 is handled with track level protection.

I am old school and would have estimated my configuration to be 7 data and 1 parity. Therefore, I expected to have 18824 GBs of useable space.

How does parity for RAID 5 work with track level protection?

[chiodp · Accepted solution]

In your post you refer to Vmax , Vmax is a symmetrix on the clariion we format the disk at 520 block and not at 512kb .

You need to post your question in the symmetrix forum ....
Regards
Pierluca

[RRR]

A small side note:

400GB = 400,000,000,000 bytes
When you calculate it back to base 2 Gigabytes (also called binary Gigabytes) it makes the following:
400*1,000,000,000/1024/1024/1024 = 372 GiB not 382 !

On a Clariion that would be 366GiB since sectors are made of 520 bytes instead of 512.