Reconfiguring server, RAIDZ1 or RAIDZ2?

[MatDef]

Since I have to reconfigure my server anyway to upgrade to FreeNAS 8.0.1, I figured I might as well redo the zfs setup at the same time. RIght now the server specs are as follows:

Intel Atom D510
4gb DDR2 667mhz
6x3TB WD GP hdd's

It's currently setup as two separate raidz1 vdev's, which works fine but has me a little limited on space. So my question is this:

Should I just go with a 6 drive raidz2 array, or is raidz1 enough? I could use the extra space, as I only have 24% free remaining and can't add any more drives (case is a Lian-Li Q08), but I'm not sure if it's a smart idea for data integrity (as they are GP drives, and probably aren't the most reliable in the world).

Thanks in advance.

 

[Rowens]

How good is your backup of the data? If it's good, and you really need the extra space, go with raidz1. If it were me though, I'd go with raidz2. When the 1st drive goes bad, you can survive 1 more drive failure without data loss (and if one of the 5 surviving disks is marginal, the stress of resilvering may be enough to push it over the edge). The extra margin could make the difference between a temporary server slowdown and a restore/rebuild.

 

[MatDef]

How good is your backup of the data? If it's good, and you really need the extra space, go with raidz1. If it were me though, I'd go with raidz2. When the 1st drive goes bad, you can survive 1 more drive failure without data loss (and if one of the 5 surviving disks is marginal, the stress of resilvering may be enough to push it over the edge). The extra margin could make the difference between a temporary server slowdown and a restore/rebuild.

I'm basically reduced to drag+drop right now to a whole bunch of individual 2tb drives, if anyone has a better idea on how to back it up I'd love to hear it (I only have one other server, which is a win2k8r2 box with 2 drives).

 

[davros123]

definitely raidz2.

 

[TheMTZ]

definitely raidz2.

This.

 

[young_einstein]

Should I just go with a 6 drive raidz2 array, or is raidz1 enough? I could use the extra space...

I'm a little bit confused by this comment!

How is switching from 2 RAID-Z pools to a single RAID-Z2 going to give you any extra space?

Your total capacity is still going to be exactly the same either way, isn't it?!?

RAID-z is n-1 capacity, IE -
3 x 3TB = 9TB (raw capacity) - 1 x 3TB (redundancy) = 6TB usable space

Double that again if you're running 2 pools, and you end up with 12TB usable space.

RAID-Z2 gives you n-2 capacity, IE -
6 x 3TB = 18TB (raw capacity) - 2 x 3TB (redundancy) = 12TB usable space.

You don't gain any space running a single RAID-Z2 vs two RAID-Z ...

EDIT: So ... given that there's really no space advantage one way or the other, the obvious answer is that you'd be completely silly not to do RAID-Z2.

 

[Tak Ne]

I read it as...

They're rebuilding a fileserver so should they change the zfs pool structure while they're doing it?

If you're considering using a 5+1 Z1 instead of 4+2 Z2 its a matter of how big a risk you want to take.
If your data is backed up and easy to restore then go ahead, especially considering you're running low.

As you said, Raid-Z2 offers no more space than the previous setup but a lot more redundancy.

 

[MatDef]

I'm a little bit confused by this comment!

How is switching from 2 RAID-Z pools to a single RAID-Z2 going to give you any extra space?

Your total capacity is still going to be exactly the same either way, isn't it?!?

RAID-z is n-1 capacity, IE -
3 x 3TB = 9TB (raw capacity) - 1 x 3TB (redundancy) = 6TB usable space

Double that again if you're running 2 pools, and you end up with 12TB usable space.

RAID-Z2 gives you n-2 capacity, IE -
6 x 3TB = 18TB (raw capacity) - 2 x 3TB (redundancy) = 12TB usable space.

You don't gain any space running a single RAID-Z2 vs two RAID-Z ...

EDIT: So ... given that there's really no space advantage one way or the other, the obvious answer is that you'd be completely silly not to do RAID-Z2.

I read it as...

They're rebuilding a fileserver so should they change the zfs pool structure while they're doing it?

If you're considering using a 5+1 Z1 instead of 4+2 Z2 its a matter of how big a risk you want to take.
If your data is backed up and easy to restore then go ahead, especially considering you're running low.

As you said, Raid-Z2 offers no more space than the previous setup but a lot more redundancy.

I originally had 3x3tb in a raidz1, I added another 3x3tb to the pool in another vdev later on. The only reason I'm asking is because I can't upgrade or import my pool into the 8.x FreeNAS releases, so I'm going to scrap everything and start again. I know raidz2 won't make any size changes, I was just wondering if it's worth the risk of going with the single parity drive in raidz1. Since the answer has been pretty much 100% no, I'm going to stick with raidz2 and hope that the 4tb drives come out sooner rather than later.

 

[brutalizer]

Rebuild time with large disks can take very long time. With future 5TB disks, it can take weeks maybe? During that time, the raid will be stressed so it can show read errors -> you lost all data.

With large disks, rebuild times will take long time. Therefore, use raidz2. With really really really large disks, use raidz3.

 

[danswartz]

Another option (if disks are cheap): go with 3-way mirrors. If you need more space, you can stripe several of these together.

 

[Rowens]

I'm basically reduced to drag+drop right now to a whole bunch of individual 2tb drives, if anyone has a better idea on how to back it up I'd love to hear it (I only have one other server, which is a win2k8r2 box with 2 drives).

If you can back up to another dedicated server, that's the best option. Also the most expensive and probably outside the budget.

Short of that, you could use external drives in USB or (better) ESATA enclosures, or spare space on another computer. Some methods to look at:

• zfs send
• rsync
• robocopy (if you'd rather use MS-Windows tools)
• ntbackup + task scheduler (if you *really* want to use MS-Windows tools )

zfs send is *fast* if your systems support it. But if you're storing the backup on a Windows box, rsync or robocopy would probably do the trick.

 

[Aesma]

Obviously the data is entirely backed up since he will destroy the pools. Sure, having a bunch of drives on a shelf is not the nicest way of doing it, but it works.

 

[MatDef]

If you can back up to another dedicated server, that's the best option. Also the most expensive and probably outside the budget.

Short of that, you could use external drives in USB or (better) ESATA enclosures, or spare space on another computer. Some methods to look at:

• zfs send
• rsync
• robocopy (if you'd rather use MS-Windows tools)
• ntbackup + task scheduler (if you *really* want to use MS-Windows tools )

zfs send is *fast* if your systems support it. But if you're storing the backup on a Windows box, rsync or robocopy would probably do the trick.

Obviously the data is entirely backed up since he will destroy the pools. Sure, having a bunch of drives on a shelf is not the nicest way of doing it, but it works.

I already did a full backup and am busy restoring the data right now, it should be done sometime tomorrow.

I still have 5 or 6 2tb drives and 2 4-bay sans digital esata units sitting in the closet, I suppose I could put those into a setup. Should I setup another pool and clone one to the other?

 

[Rowens]

I still have 5 or 6 2tb drives and 2 4-bay sans digital esata units sitting in the closet, I suppose I could put those into a setup. Should I setup another pool and clone one to the other?

That would probably work well. At work I'm doing something similar using zxfer (c.f. http://code.google.com/p/zxfer/) and zfSnap (c.f. https://github.com/graudeejs/zfSnap), cloning from internal drives to external enclosures.

Whatever setup you come up with, make sure you've thought about what you'll do if your current server dies (e.g. if your motherboard takes up smoking). An external enclosure with all your data plus a bootable CD/DVD/flash drive could probably get you going again, assuming you have another box which can be pressed into service as a temporary server. Just make sure you test it at least once; it would be annoying to find out too late that (for example) you need a port-multiplier-compatible eSATA card because the onboard controller can't talk to your enclosure.