Raidz2, 3 VS. Mirrored for backup storage critical

[iHeartMacs]

Hi,

I'm new to ZFS and I'm building my first Freenas Backup Server. I so many of you are great at helping me with my build I thought I'd start another thread just about Raid to keep it simple and maybe help out someone else searching the forum.

My Question is: What are your suggestions for Raid with a system capable of 14 drives in a Supermicro 4U and using a
Supermicro Motherboard Micro ATX DDR4 LGA 1151 X11SSL-CF-O

MOBO link: https://www.amazon.com/Supermicro-M...1-1&keywords=Supermicro+X11SSL-CF&tag=ozlp-20

Information about environment: This system will be accessed by PC's and Mac's with backup software respective to there OS. (TIme Machine, Windows 10 Backup, etc.)
As you know TimeMachine is not easily configurable to be on a schedule so about 6 computers could possibly try to back up at the same time. That's just the Mac side.

Hopeful Requirements: I would like to have at least 48TB of usable storage for backups. I know there is trade off's with how many pools and vdevs. I've done plenty of digging but I think I need the ah ha moment about this subject. Here is my Noob understanding.

If I do mirrored I get better redundancy at a performance loss.
Q-1: If I wanted to be safe do I setup each pair of mirrored Drives as a Pool. 2=Drives = 1 pool
(my understanding with mirrored is if there are more drives in the pool and I lose 1 or 2 then I lose the whole pool if they are on the same vdev)

Q-2: With Raidz2,Raidz3 I can get more performance at greater risk of Data loss. Is Raidz3 an acceptable configuration for critical data storage (backups)
(obviously not doing Raidz1)

Q-3: If I do Raidz3 that means I need three drives for parity. The 4U can hold 14 drives. That means If I did one SSD for boot I would have 1 SATA slot left on MOBO. So I could do 12 Drives and 3 for parity?

Thx for any advice. I'll do the research if you make suggestions

 

[danb35]

system capable of 14 drives in a Supermicro 4U

Why do you think your proposed SC846-E16 only supports 14 drives? It supports 24.

If I do mirrored I get better redundancy at a performance loss.

No, you've got this backward. Mirroring is worse for redundancy, but (with multiple striped mirrors) better for performance.

If I wanted to be safe do I setup each pair of mirrored Drives as a Pool.

Only if you want to make system administration much more difficult for yourself.

With Raidz2,Raidz3 I can get more performance at greater risk of Data loss.

Sequential reads may be faster with RAIDZn, but random I/O won't be. Time Machine does lots of random I/O. And RAIDZ2 or RAIDZ3 have better redundancy than a system of striped mirrors, in that the pool will survive the failure of any two (or three) disks. With a pool consisting of, say, seven mirrors striped, the pool could survive the failure of up to seven disks, but it could also be completely lost with two failed disks if they were the "wrong" two disks.

The 4U can hold 14 drives.

As noted above, no, it can hold 24. And there's no reason that the boot SSD needs to occupy one of them--SuperMicro sells a bracket to let you install that as a fixed disk, or you could even just Velcro it to the side of the case.

 

[Ericloewe]

As noted above, no, it can hold 24. And there's no reason that the boot SSD needs to occupy one of them--SuperMicro sells a bracket to let you install that as a fixed disk, or you could even just Velcro it to the side of the case.

And some models even have 2.5" bays next to the PSUs for hot-swappable SSDs.

 

[brando56894]

What @danb35 said. I used mirrors for about a year or two and it does make upgrading/resilvering quicker and the performance is better, but it does have a major fail point which RAIDZ doesn't, so if protection is your main focus go with RAIDZ2/3. Also RAIDZ will give you more storage space, since mirrors effectively half your available storage.

As for storing the OS, you could easily use a SATA DOM instead of USB/SSD/HDD. It'll be (about) the same size as a flash drive but a lot faster, and won't take up any of your bays, they tend to be a bit expensive though :-/

 

[iHeartMacs]

Why do you think your proposed SC846-E16 only supports 14 drives? It supports 24.

Oh what the heck! The hardware beginners guide says the 4U only holds 14. Should have looked at the specs.

Sequential reads may be faster with RAIDZn, but random I/O won't be. Time Machine does lots of random I/O. And RAIDZ2 or RAIDZ3 have better redundancy than a system of striped mirrors, in that the pool will survive the failure of any two (or three) disks. With a pool consisting of, say, seven mirrors striped, the pool could survive the failure of up to seven disks, but it could also be completely lost with two failed disks if they were the "wrong" two disks.

About this.. So what raid should I use for random I/O? In regards to what Raid system I use for random I/O, I'm reading that I want either a set of 6 or 12 disks. What does that mean? 12 hard drives plus 3 for parity? If I want more than 12 do I do another 6 and then still 3 for parity?

As noted above, no, it can hold 24. And there's no reason that the boot SSD needs to occupy one of them--SuperMicro sells a bracket to let you install that as a fixed disk, or you could even just Velcro it to the side of the case.[/QUOTE]

I knew the SSD would not occupy the 4U spaces. I thought that the ssd would attach to the MOBO and then put it somewhere in the case so I wasn't off on that but I still am foggy about how many SATA ports the case uses for 24 disks?

how does the Case connect to the MOBO. Someone mentioned breakout cables. Does every drive in the case have a sata connection that somehow goes to the MOBO or is there a controller of some sort in the case? What I'm asking is how many SATA ports will be used on the MOBO for the 24 disk CASE?

In regards to what Raid system I use for random I/O, I'm reading that I want either a set of 6 or 12 disks. What does that mean? 12 hard drives plus 3 for parity? If I want more than 12 do I do another 6 and then still 3 for parity?

Looks like I'll be reading more on this forum. Thanks for the enlightenment.

 

[danb35]

I still am foggy about how many SATA ports the case uses for 24 disks?

None; it uses one SAS connector. The motherboard you've chosen has those onboard, so you just need a SAS cable from the motherboard to the backplane in your chassis. See https://forums.freenas.org/index.ph...-sas-sy-a-primer-on-basic-sas-and-sata.26145/

Oh what the heck! The hardware beginners guide says the 4U only holds 14. Should have looked at the specs.

Where exactly are you seeing that? Not sure if you're misreading it, or if there's a typo there--but in any event, it isn't correct.

I'm reading that I want either a set of 6 or 12 disks. What does that mean? 12 hard drives plus 3 for parity?

No, six disks, (the capacity of) two of which will be parity (in a RAIDZ2 arrangement, which is what I'd recommend). With twelve disks, you'd use two sets of six, and the capacity of two disks in each set would be used for parity. And, as "(the capacity of)" indicates, RAIDZn doesn't use dedicated parity disks; the parity is distributed across the vdev.

 

[danb35]

Just for clarity, here's the link to the product page for the chassis you mentioned in your other thread. It's a very good choice (albeit expensive if bought new), but it doesn't sound like you have a very good idea of its capabilities yet.

 

[Ericloewe]

The hardware beginners guide says the 4U only holds 14.

What document are you looking at? The Hardware Recommendations Guide doesn't say that.

 

[iHeartMacs]

What document are you looking at? The Hardware Recommendations Guide doesn't say that.

https://forums.freenas.org/index.php?resources/freenas®-quick-hardware-guide.7/

Hi sorry it says 14 drives under the motherboard. I know you can add more drives with expansion so I think I was just tired putting the list together. Thanks for helping me see my error.

 

[iHeartMacs]

Just for clarity, here's the link to the product page for the chassis you mentioned in your other thread. It's a very good choice (albeit expensive if bought new), but it doesn't sound like you have a very good idea of its capabilities yet.

For sure. I have no idea. I'm mostly a networking, Data recovery, and security guy. That's why I really appreciate all the insight on this forum. This forum is actually one of the most helpful forums that I'm on now and I'm on many for sure. (good ones too) not only do the responses come from what seems like really knowledgable members but members who actually want to help. Thx again and again. I'm totally going to try and give back by posting my results and build.

 

[iHeartMacs]

None; it uses one SAS connector. The motherboard you've chosen has those onboard, so you just need a SAS cable from the motherboard to the backplane in your chassis. See https://forums.freenas.org/index.ph...-sas-sy-a-primer-on-basic-sas-and-sata.26145/

Where exactly are you seeing that? Not sure if you're misreading it, or if there's a typo there--but in any event, it isn't correct.

No, six disks, (the capacity of) two of which will be parity (in a RAIDZ2 arrangement, which is what I'd recommend). With twelve disks, you'd use two sets of six, and the capacity of two disks in each set would be used for parity. And, as "(the capacity of)" indicates, RAIDZn doesn't use dedicated parity disks; the parity is distributed across the vdev.

Oh wow. OK! Lightbulb. There are no extra disks for parity. BING* got it now. That right there clears up some more confusion. It's amazing how one piece can make an entire puzzle fall into place. Also see above for why I thought the Case had only 14 drive bays.