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What is the useable capacity on RAID 5 (7+1)?
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?
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
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September 22nd, 2009 11:00
You need to post your question in the symmetrix forum ....
Regards
Pierluca
RRR
5.7K Posts
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September 23rd, 2009 03:00
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.