Maximum recomended disk size for a RAID-Z2 pool

[Miguel Nunes]

Hi everyone.

I have a question regarding ZFS.

What is the recomended maximum size of each disk on a RAID-Z2 pool with 4 disks?

I am currently using a HP Micro-server with 16GB of ECC RAM for backup only. It is basically a backup system without load.

Thank you in advance,

Miguel

 

[DrKK]

If you have 4 disks, in a RAID-Z2 pool, that is 50% parity. 50% is EXTREMELY conservative. You can run whatever you like in that sir, without taking much risk.

Also, since it's a backup, the rules are even relaxed from that.

You are not even close to a problem. Proceed sir.

 

[Miguel Nunes]

If you have 4 disks, in a RAID-Z2 pool, that is 50% parity. 50% is EXTREMELY conservative. You can run whatever you like in that sir, without taking much risk.

Also, since it's a backup, the rules are even relaxed from that.

You are not even close to a problem. Proceed sir.

Thanks. Iam thinking in 4 x 8TB to store timemachine (3 macs), nfs folders for ubuntu (just as a source of files, not compiling over nfs) e maybe one iscsi with low load for my ocasional Windows.

Once again, thanks.

 

[DrKK]

These are the kinds of things people that have virtualized FreeNAS, not a real FreeNAS, say.

If in fact you have virtualized FreeNAS, then, you may have quite a few other concerns about how to configure your pools. A RAID-Z2 may not be appropriate in that case. You'll have to talk to someone who knows more about the ramifications of virtualization.

 

[Chris Moore]

You say this:

for backup only. It is basically a backup system without load.

Then you totally contradict yourself with this:

Iam thinking in 4 x 8TB to store timemachine (3 macs), nfs folders for ubuntu (just as a source of files, not compiling over nfs) e maybe one iscsi with low load for my ocasional Windows.

If you want to run iSCSI to Windows, you are not talking about a backup any more. You can use as large a disk as you want, but in a RAIDz2 vdev, you obtain roughly the performance of the slowest member disk. If you want more IOPS, which is usually desirable with iSCSI, you will want more vdevs. In such a small system, the best you can do is two mirror vdevs.
Good luck.

 

[Miguel Nunes]

You say this:
Then you totally contradict yourself with this:

If you want to run iSCSI to Windows, you are not talking about a backup any more. You can use as large a disk as you want, but in a RAIDz2 vdev, you obtain roughly the performance of the slowest member disk. If you want more IOPS, which is usually desirable with iSCSI, you will want more vdevs. In such a small system, the best you can do is two mirror vdevs.
Good luck.

Hi Chris,

I know what you mean :) When I said baclup I meant a system with really small load.

I have heard that for example RAID-5 should not use HDDs over 1TB because there might be a failure when rebuilding.

The system is really low performance, but the machine is so stable that I would like to use it as a small load device.

Thanks for your help.

 

[Chris Moore]

The system is really low performance, but the machine is so stable that I would like to use it as a small load device.

The problem is, iSCSI changes every design principle. It really needs a whole separate discussion from regular file storage.

 

[Miguel Nunes]

The problem is, iSCSI changes every design principle. It really needs a whole separate discussion from regular file storage.

AH okay Chris... I think I know what you mean. Lets remove iSCSI of the equation.

My question arrised from the fact I have read somewhere that systems with one redundant disk are prone to a rebuild issue where there might be an unrecoverable error that pops before the rebuild is completed. So I was wondering what would be the recomended size for a setup with 2 redundant disks.

Meanwhile I have a networking issue that I need to tackle. Not enough money to buy the new HDDs now.

Setup:
HP Microserver Gen 7
16GB of ECC Ram
HP BMC board
4 x 500GB disks with 2 redundant discs.
Melanox ConnectX-3 infiniband card.

 

[tngri]

Ok, so after all these considerations, I would ask again (that's topic after all)
What is the maximum recommend size of each HDD for an RAIDZ2 ?
It's been told that RAIDZ with 3TB is dangerous, wha about RAIDE2 ?
I see people seting up pool with 8TB I wonder if that's ok or not ...

thanks

 

[SweetAndLow]

Depend on how long a rebuild takes. Current drive sizes should still be fine, imo.

 

[Chris Moore]

What is the maximum recommend size of each HDD for an RAIDZ2 ?

There really is no maximum size for the individual drives. We just built a new server at work using 12TB drives and I know of others that have used larger drives. I prefer to keep the width of each vdev in the pool to 6 drives because this helps with rebuild time, but not because there is some limitation. We had someone come to the forum a couple years ago that had inherited a system that was built by a previous employee of their company and it was built with 45 drives in a single vdev at RAIDz2 redundancy. That storage would not have performed well, but it worked. Many of the design considerations we use are geared toward providing the best performance and reliability.

It's been told that RAIDZ with 3TB is dangerous, wha about RAIDE2 ?

The general guidance of the forum for several years now has been to use RAIDz2 with anything larger than a 1TB drive. Larger drives increase rebuild times.

I see people seting up pool with 8TB I wonder if that's ok or not ...

Some people are using RAIDz3 out of an abundance of caution, but I still find RAIDz2 acceptable however that is with pre-tested spares on hand to perform a replacement as soon as a replacement is needed. I do not need to wait for the acquisition of a replacement drive.

Here are some good resources that you should review if you have not already:

Slideshow explaining VDev, zpool, ZIL and L2ARC
https://www.ixsystems.com/community...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

Terminology and Abbreviations Primer
https://www.ixsystems.com/community/threads/terminology-and-abbreviations-primer.28174/

Why not to use RAID-5 or RAIDz1
https://www.zdnet.com/article/why-raid-5-stops-working-in-2009/

Building, Burn-In, and Testing your FreeNAS system
https://www.ixsystems.com/community/resources/building-burn-in-and-testing-your-freenas-system.38/

GitHub repository for FreeNAS scripts, including disk burnin
https://www.ixsystems.com/community...for-freenas-scripts-including-disk-burnin.28/

solnet-array-test (for drive / array speed) non destructive test by @jgreco
https://www.ixsystems.com/community/resources/solnet-array-test.1/

Useful Commands
https://www.ixsystems.com/community/threads/useful-commands.30314/#post-195192

Hard Drive Troubleshooting Guide (All Versions of FreeNAS)
https://www.ixsystems.com/community...bleshooting-guide-all-versions-of-freenas.17/