Mac Pro 2,1 - 3 drive software RAID 5

thedarkhorse said:

At work I am getting a new 20TB raid box (thunderbolt, firewire, usb3) and will be migrating most of my data over to it, doing this is going to free up some drives from an aging NAS. Can I put 3 drives in software RAID 5 in the mac pro 2,1(internally). I've done software 2 drive RAID 0 and RAID 1 in a mac pro, just not RAID 5. I will not be using this for OS, the 4th bay is my OS drive.

I tried googling this but couldn't find this specific situation of 3 internal drive soft raid 5.

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You cannot create RAID-5 using Disk Utility which you probably did when creating RAID-0 and RAID-1 previously. However, there may be 3rd party software RAID drivers which can be purchased that can create a soft RAID-5 in the Mac Pro.

Why do you want internal RAID-5 as opposed to a speedy RAID-0 system with external backup? Keep in mind that RAID-5 is not in itself a backup, you still need to have at least 2 completely separate copies of your files. The RAID-5 just protects your main or backup system from a disk failure. I use RAID-0 SSD as my main drive, and a RAID-5 external system as DAS Time Machine backup, and a RAID NAS as secondary remote Time Machine backup. I also have CCC programmed to do a nightly clone of my boot/system drive.

I use MacZFS 74.3.3 with a 4 drive RAIDZ array, backing up to a FreeNAS box. Software RAID has a nasty habit of failing over time, and hardware RAID requires controllers and enterprise drives, ZFS for the win

hfg said:

Why do you want internal RAID-5 as opposed to a speedy RAID-0 system with external backup? Keep in mind that RAID-5 is not in itself a backup, you still need to have at least 2 completely separate copies of your files. The RAID-5 just protects your main or backup system from a disk failure.

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Sorry for bumping up an old thread, but I was researching software RAID 5 and this caught my eye.

It doesn't matter if the array is internal or external to the computer. The need for some protection is the same, and you answered your own question in your reply.

The need or desire for RAID-5 isn't about a backup. It's about reducing the impact of a failure. If I create my disks in a speedy RAID-0, as you suggested, then a disk failure (which will eventually happen) completely puts me out of business. I have to replace the disk AND restore from the backup before I'm able to continue.

With RAID-5 (or some other variants), you don't have to go through that type of restoration process. Slap in another drive and rebuild.

I'm not against speedy RAID-0, but I prefer using that for my backup drives and keeping my operational work on RAID-5. As I mentioned before, it's immaterial whether that array is internal or external.