I've got 2 Venus DS-DS3RPRO eSATA/USB 2.0 2x1TB RAID1 units on my MacBook Pro that can be repurposed for Time Machine use. (I'll use at least one of them for that purpose with the boot SSD disk I'm about to order.)
So long as there' sufficient capacity, they should work (just don't use them in stripe mode
).
But yeah, that brings up why I'm leaning towards playing it safe and just going with two 2x2 TB RAID1 Volumes in the 4-disk Apple RAID setup. Right now with the Venus units I'm not worried about backups because they're mirrored, that was the whole point
Lose a disk, pop in a new one, no worries. (Haven't lost one yet, either. Knock on wood. I can also lose one of the units because if it fails, I can pop the disks out and pop them into the other unit if I really need to get at the data. Ah, redundancy
)
If you're going to set up a pair of mirrors, stripe the pair to allow for additional throughputs as well. Unfortunately, this will only provide
n/2 usable capacity (the "catch").
Also,
no matter what your storage configuration, there is no substitute for a backup solution. It doesn't matter what RAID level or how much failover has been designed into the system (including the most sophisticated SAN that could ever be concieved). You still need a backup.
One obvious thing that won't be covered in your intent on running a pair of mirrors, is user error, such as an accidental file deletion as it's performed on all members of the mirror.
Now if you mean to use 1 mirror for primary data, and another as a backup (not RAIDed together, but only via backup software), then that will be fine. Tad overkill for a home system, but won't cause any harm.
If I were to RAID5 the 4 disks I'd be a LOT more nervous about that. I want at least 4 usable TB out of the setup and maybe peace of mind is worth sacrificing the ~1.5-1.6 extra TB I'd have if I went to RAID5. I don't want to buy more disk to back up all of these drives, that was sort of the point of having the system be maxed out to begin with.
Nothing to be nervous about so long as you use enterprise disks (this could be a real issue if you were to use consumer grade disks).
RAID 5 does provide a nice balance of capacity, speed, and redundancy. Greater redundancy would cut your usable capacity and speed (i.e. RAID 10 or 6 for example). They all have their uses of course, but for a system you've physical access to on a daily basis, you will be able to replace a defective drive in order to allow for a rebuild.
Now if this system were a remote server OTOH, then RAID 5 wouldn't be the way to go (better to go with 10, 6, or some sort of nested configuration with at least one hot spare).
For cheap backup, you could opt for an eSATA based Port Multiplier enclosure (
4 bay example), and JBOD the disks (granted, if a disks fails, the data's not accessible). But the viable disks remaining can be recovered by software utilities (i.e. Disk Warrior), so only the data on the defective disk actually disappears (which would be recoverable from the primary storage location). It's better than a stripe set IMO, as in an absolute total disaster (both the backup and primary locations are damaged <primary = completely unrecoverable>, most of the data is retained <all but the one disk>). If such a disaster were to happen and the backup a stripe set, you're data's gone. End of story.
By your Newegg comment, did you mean all the product comments from people buying disk drives from them?
Yes.
I read through the reviews, and try to determine if they were DOA or returned quickly due to other issues (i.e. need to read all of them, as there are those that will give more than 1 or 2 eggs due to newegg's return policy). Then compute the failure %.
