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Deciding between RAIDZ2 and RAIDZ1

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Feb 23, 2018
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#1
So im planning to setup a new pool for my FREENAS Server

System
Intel(R) Xeon(R) CPU E31270 @ 3.40GHz
24GB ECC RAM
10GB Ethernet
20 x 4TB Drives

So i have currently setup a mirrored vdev of my 20 x 4TB drives but the cost of storage has become a lot and can't be barred so shifting to RAIDZ for more usable space.
From my googling experience i have come to know that RAIDZ doesn't support expansion (yet) and secondly greater the amount of vdevs means greater the performance
So keeping these 2 points in mind i have 2 ways of setting up my RIADZ pool

Option 1 - RAIDZ2
2 Vdevs of 10 x 4TB drives each
- assumed con : - to increase space i mite need 10 more drives to add another vdev

Option 2 - RAIDZ1
4 vdevs of 5 drives each
: - in this i can expand storage with another vdev of 5 drives

Both options will have 4 parity drives so i guess reliability should be same
Please correct me if i have made any non technical assumption as i'm not an expert
Suggest which option i should go to for better reliability and performance
TIA
 

sretalla

FreeNAS Expert
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#2
Both options will have 4 parity drives so i guess reliability should be same
No, not the same.

If you lose 2 drives in the same VDEV... Option 1, no problem. Option 2 pool is dead.

Your choice (although the wisdom in the forum is that with 4TB drives, you don't really have any viable option for RAIDZ1), will depend on how much you want to keep your data.
 
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#3
Option 1 - RAIDZ2
2 Vdevs of 10 x 4TB drives each
You may consider 12-drive vdevs. If I recall correctly, RAIDZ2 makes the most efficient use of space when the vdevs are multiples of 6 disks.

- assumed con : - to increase space i mite need 10 more drives to add another vdev
I think this depends on your use case. If this is an enterprise or business use case you may consider keeping the vdevs all the same type and number of disks. There has been suggestions that doing so may help prevent odd issues due to mismatches. For home use however I think you'd be fine adding smaller vdevs if you'd like, for example 6-disk vdevs. TBH I haven't tested this out personally though so you may want to research it a bit more.
 

Jessep

FreeNAS Experienced
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#4
You may consider 12-drive vdevs. If I recall correctly, RAIDZ2 makes the most efficient use of space when the vdevs are multiples of 6 disks.
This is no longer true mostly due to compression and changes in the backend. There is an article that explains it in detail that I'm not finding in a quick search.
 

HoneyBadger

Mushroom! Mushroom!
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#5
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#6
Thanks for digging up that link!
 
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Feb 23, 2018
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#8
Thanks for the help, i guess will go with raidz2 then. Making vdev of 6 drive each will add a lot of parity disks, option 1 seems more viable in my use case. As per the shared article multple of 6 drives isn't a must for raidz2 but min 6 drives is recommended so 2 vdev of 10 x 4tb drives each. Will add 1 spare drive to the pool to for quick recovery of 1 drive failure.
I do have a backup freenas server as well which is setup for daily zfs replication, this should further minimize data loss
 
Last edited:

Bhoot

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#9
I would still recommend a 12 disk raidz3 if you have the space and resources. RaidZ1 should be stopped by FreeNAS officially, might as well have no backups.
 
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#10
RaidZ1 should be stopped by FreeNAS officially, might as well have no backups.
I'm not sure it is all that bad :) . Some folks have different budgets, build sizes, tolerances for data loss etc that might justify it in their case. Some drives are even an order or magnitude better in terms of URE rate which helps somewhat; for example Seagate's Iron Wolf line reports 1:10^15 rather than 1:10^14 as reported in the infamous article. For example, imagine someone storing some music and movie rips off disks they already own. They may want some redundancy but if it totally bites the dust they are just out some time re-ripping their content.
 
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