What is This RAID?

[TD4]

Hi,

I read a review for an ASUSTOR NAS some months ago that I kept open on my phone, until my wife decided I had too many tabs open and closed them all.

I've read tons about different RAID configurations, but I haven't found this one anywhere.

I think they set up a four disk array with 1 SSD for speedy read/writes, 2 mirrored HDDs, and 1 spare HDD that gets written to if one of the mirrored drives failed.

Is this something that is possible, or did I misunderstand it?

It seemed like the best possible option.

There is a chance it could have been RAID 5, with 2 striped rather than mirrored drives, but I think the option I described would be better.

EDIT AGAIN:

I think I found it, and I misunderstood what they were getting at:

"http://www.guru3d.com/articles-pages/asustor-as6404t-nas-review,8.html

You could set up:

• 1 x 1 TB SSD for OS and APP related functionality to get the best performance out of the NAS.
• 3 x 2 TB set up in RAID5 for a bit of long time storage paired with redundancy (the raid array will allow for one HDD failure).
• 1 x 2 TB set up as hot-spare. If one HDD dies, this hot-spare will kick in and repair the array to a normal functioning one, hence that is a little extra safety for your data.

In the screenshot you can see the SSD storage unit listed, we have already set up the SSD. If you wanted to go JBOD or RAID 0/1/5 you can use the volume setup wizard here. There is a lot of flexibility, you could just use 4 HDDs in RAID5 but also go for, say, RAID5 in a 3+1 hot-spare configuration so when one HDD fails, the hot-spare kicks in automatically and repairs the array. But you can also mirror and stripe (RAID 0/1) or simply build a huge JBOD unit and get yourself one massive volume."

So, with RAID 5 with 4 disks, you can't do 1 TB SSD + 2 Mirrored + 1 hot spare, It would have to be striped, not mirrored.

 

[dave_the_nerd]

Mirrored (RAID-1), Striped (RAID-0), and RAID-5 (Striped + Parity) aren't the same thing. You could absolutely do a simple 2-drive mirror (RAID-1) and have a third drive as a hot spare. But that's kind of silly.

But for a 4-disk NAS that you intend to use for production work, your best bet is a 4-drive RAID-10 and a "cold spare" in a desk drawer, to swap out in case of drive failure. Rebuilds will be fast because you're not using parity. SSD will be bottlenecked by the ethernet connection, so there's little benefit.