Pros/Cons putting RAID 1 on Port 1 & Port 2 of drive array?

[Robert Simons]

Hello all.  I have a new DL360p Gen 8 server with a P420i Smart Arry controller.  This controller has 2 ports, drives 1-4 connect to Port 1 & drives 5-8 connect to Port 2.  I am going to setup a RAID 1 array for my VMware OS & a RAID 5 array for the VMware datastore.

My question is, are there any pros/cons if I were to setup my RAID 1 array using 2 different ports on the array controller, drive bays 1 & 5?  Looking for performance & redundancy pros/cons.

Thanks,

Robert

[ernst limbrunner]

hi

redundancy-wise it is better to have both raid 1 disks on two channels (bay 1 and bay5).

this will survive a cable error in adition to a disk failure.

the problem is the raid5 disks. it is recommended not to spread them when possible.

one example:

you have all 4 disks of a raid 5 on one channel. probability that if a certail channel fails is 50% that you will survive.

with 5 disks it works out the same if the 5th disk is on the failed channel.

if you have two or more disks of a raid 5 on different channels, a channel failure will kill your raid5.

so if you plan for a raid 1 and up to 4 raid 5 disks put the raid 1 disks in 1 and 5 and the raid 5 disks in 2,3,4 and 6.

for more than 5 raid5 disks, you might have a 100% loss if one channel fails.

the smart conrollers became more clever lately and even a channel failure can often be recovered,

however this is not guaranteed.

as far as performance is concerned, there is no difference. the controller sees 8 separatesas  ports (no matter in which bay they are used) and treats them equally (as long as all 8 ports go to the same controller).

best regards

ernesto (germany)