vnx5300: double fault redundancy ?

Hello,

I've a VNX5300 equipped with 50x HDDs (600GB each).

Bus0 Enclosure0 has:

•                     d0, d1, d2, d3: reserved

•                     d4: raidgroup 100 hot spare

•                     d5..d13: raidgroup 1 (9x hdd)

•                     d14..d22: raidgroup 2 (9x hdd)

•                     d23..d24: raidgroup 3 (2x hdd)

Bus1 Enclosure0 has:

•                     d0..d6: raidgroup 3 (7x hdd)

•                     d7..d15: raidgroup 4 (9x hdd)

•                     d16..d24: raidgroup 5 (9x hdd)

So I have a total of 5 * RAID5 (8+1) which as capacity totals of: 5 * (500*8) = 5 * 4000 = 20TB which match my current capacity.

Now the question I've for you is the following... I'm experiencing a bad HDD in B0E0D10 (raidgroup1) and the system is currently using d4 as hot spare. I was expecting instead that the faulted drive was taken care by its RAID5 first and the d4 in case of double fault.

Can anyone share some more light on the fault logic used by this VNX5300 ?

Thank you,

A.