Different drive size?

[rangopango]

Is it a good idea to use four 8TB drives and one 1TB for RAID6?

Could I replace the 1TB with 8TB in RAID6 if I have two 8TB parity drives without losing all of my data?

 

[m0nkey_]

Is it a good idea to use four 8TB drives and one 1TB for RAID6?

There is no such thing as RAID6 in ZFS. You probably mean RAIDZ2. Probably not, you're going to lose 7TB capacity of each 8TB drive.

 

[rangopango]

Why would I lose 7TB for each 8TB drive with one 1TB drive in the array? :O

 

[danb35]

Why would I lose 7TB for each 8TB drive with one 1TB drive in the array? :O

Because of the way RAIDZ2 works. The same would be true if you were able to put them all into a RAID6 array. The arrangement you're proposing would give you about 3 TB of usable space for 33 TB of disks. Unless you expected to be able to replace the 1 TB disk with another 8 TB disk very soon, not a good idea. And in any event, it sounds like you have some reading to do about how ZFS works.

 

[m0nkey_]

Why would I lose 7TB for each 8TB drive with one 1TB drive in the array? :O

In any kind of RAIDZ scenario, the pool will be set-up using the maximum space available on the smallest drive. You'd only end up with an array of 2TB in size with 4 drives in RAIDZ2.

Suggest you read this slideshow: https://forums.freenas.org/index.ph...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

 

[rangopango]

Wouldn't four 8TB drives give me 13.6TB of usable data, and with one 1TB drive in the array, it'd be around 13.6TB?

 

[danb35]

Wouldn't four 8TB drives give me 13.6TB of usable data, and with one 1TB drive in the array, it'd be around 13.6TB?

No, because:

In any kind of RAIDZ scenario, the pool will be set-up using the maximum space available on the smallest drive.

 

[rangopango]

that's an interesting way of doing things... why is it like that exactly? shouldn't the parity drive with the biggest drive be the maximum size?

 

[m0nkey_]

that's an interesting way of doing things... why is it like that exactly? shouldn't the parity drive with the biggest drive be the maximum size?

Did you look at the link to the slideshow I provided?

 

[garm]

There is no “parity drive” in ZFS

 

[danb35]

that's an interesting way of doing things.

That's the way any RAID5/RAID6 or similar system (including ZFS parity RAID) does it. There is no "parity drive" in such a system; parity is spread across all disks in the vdev. Maybe you're confused by things like unRAID. You've got some reading to do.

 

[rangopango]

That's the way any RAID5/RAID6 or similar system (including ZFS parity RAID) does it. There is no "parity drive" in such a system; parity is spread across all disks in the vdev. Maybe you're confused by things like unRAID. You've got some reading to do.

No, I read about it here.
https://docs.oracle.com/cd/E19253-01/819-5461/gcviu/index.html
The equivalent of RAID6 is RAIDZ2, which is double parity

 

[danb35]

No, I read about it here.
https://docs.oracle.com/cd/E19253-01/819-5461/gcviu/index.html

I was going to ask what part of that made you think that RAIDZ works the way you think it does, but it really doesn't matter--it doesn't work that way. As @m0nkey_ already said, "the pool will be set-up using the maximum space available on the smallest drive." Data and parity are striped across all disks in the vdev (there is no dedicated parity disk, as you seem to think), and the effect of this is that the smallest disk in the vdev limits its capacity.

The equivalent of RAID6 is RAIDZ2, which is double parity

We all know that RAIDZ2 is double-parity, and we all know that RAID6 is double-parity. That doesn't mean that RAIDZ2 is RAID6, and indeed, it isn't. We insist on the distinction because it makes a difference. If you say you have a RAIDZ1 pool, we know that's a ZFS pool. If you say you have a RAID5 array, we can assume (and hope) that it's truly RAIDZ1, but it's also possible that you did something truly stupid like build a hardware RAID5 array and create a ZFS pool on top of that--and yes, we've seen this exact scenario; this isn't just a silly hypothetical.