BUILD Considering RAIDZ2 w/ 4 Drives?

[thedirtmerchant]

I'm basically copy/pasting the hardware plan from Cyberjock
MOBO: SuperMicro X9SCM-F or X10SLL+-F
CPU: mid-recommended Intel i3
RAM: 16-32GB ECC RAM
HDD: 4 WD RED 3TB
PSU: Not a cheap one
CHASSIS: Fractal Design R4 or something similar
UPS: TBD

But my subject question...Is it really silly to do Z2 w/ 4 drives?
Basically, I will be using this to store pictures, videos, documents.
I expect to use Plex to stream videos.

I have had 2 disk failures within the last 12 months. I do NOT want to lose my
data (yes, I already have a full/separate backup). So, what I read says go RAIDZ2
which usually has 6 disks. But RAIDZ1 shouldn't be used for more than 3 disks.
Or should I just go with a RAID10?

 

[jgreco]

No, RAIDZ2 with 4 disks is fine. I don't know where you get the idea that RAIDZ2 usually has 6 disks. 6 disks gives you twice the usable space of 4 disks, so it's an economically better option, but 4 drives is fine.

 

[thedirtmerchant]

No, RAIDZ2 with 4 disks is fine. I don't know where you get the idea that RAIDZ2 usually has 6 disks. 6 disks gives you twice the usable space of 4 disks, so it's an economically better option, but 4 drives is fine.

Thought I saw this as a recurring theme in the posts I've been reading "usually has 6 disks".

 

[cyberjock]

Not "usually". It is kind of the "smart" option so is frequently used because you get 50% more space for 2 more disks and most chassis can store at least 6 disks. That's the only reason why it is a common build.

There is also the old "powers of 2" thumbrule for ZFS, but that is basically useless since compression is used by default now.

 

[Ericloewe]

Between RAIDZ2 and "RAID10", if you're looking for data security, RAIDZ2 is the better option.

Whether or not it's silly to stick to four drives is for you to decide, according to your priorities.

 

[Robert Smith]

RAIDZ2 with four drives is absolutely no problem, it is slightly safer than two mirrors, as with RAIDZ2 you can lose any two drives out of the four, and still keep your data.

If you are set on four-drive system, consider scaling up to 4TB or even 6TB disks. A six-disk system would be a more conventional choice. But if you want four, that is no problem.

 

[jgreco]

RAIDZ2 with four drives is absolutely no problem, it is slightly safer than two mirrors, as with RAIDZ2 you can lose any two drives out of the four, and still keep your data.

INCORRECT. In two mirrors, the loss of any single drive results in the loss of redundancy. With RAIDZ2, the loss of any single drive leaves you with full redundancy.

That is MUCH safer for your data.

 

[HoneyBadger]

most chassis can store at least 6 disks. That's the only reason why it is a common build.

Most entry-level server boards have six SATA ports as well, which I would think is the more common reason. Gotta fill 'em all, right?

Either way the thought process of "bang for buck" is what drives it, and a six-drive RAIDZ2 is very good value for most users.

 

[nick779]

I started out with a 4 disk Z2, practically saturated gigabit ethernet with reads, and writes were generally in the 85MB/s area. Worked fine for my purposes, but I needed to rebuild, and I figured I might as well do 6 disks now for much more space.

 

[HoneyBadger]

I started out with a 4 disk Z2, practically saturated gigabit ethernet with reads, and writes were generally in the 85MB/s area. Worked fine for my purposes, but I needed to rebuild, and I figured I might as well do 6 disks now for much more space.

Pretty much any vdev configuration can saturate GbE on reads/sequential writes. It's when you get to random I/O that RAIDZ falls down; but most home users fit the former use case very closely and as such don't see the negatives.

 

[jgreco]

Well, maybe. That's more likely to be true for the newer gear, but some of the older stuff definitely craps out well before gigE speeds for seq I/O.