Disk upgrade process question

[csanii]

I have TrueNAS Core v13 installed with currently a single boot disk and single data disk for testing. I plan on buying some NAS CMR drives but thought I should ask this question so that I can properly plan out what to buy and for future upgrade planning. I searched the forums but didn't have luck finding the answers.
Example:
If I buy 2x2TB drives today I can only mirror them or have 2 single drives with no redundancy(NOT recommended).
1) If at a later date I buy another 2TB drive can I add to the existing 2x2TB pool so TrueNAS uses it as a parity disk and over time spreads the data across the 3 disks OR do I have to do a backup/restore in order to configure a 3 drive parity system ?

2) Instead of buying a 3rd 2TB drive if I buy a 4TB drive is there a way to have TrueNAS mirror the existing data on the 2x2TB mirror to the new 4TB drive and then I manually break the mirror and then manually configure the 2x2TB to be the mirror of the 4TB drive OR does this require a backup/restore OR is it not possible to mirror a single 4TB drive to 2x2TB drives?

 

[joeschmuck]

1) If at a later date I buy another 2TB drive can I add to the existing 2x2TB pool so TrueNAS uses it as a parity disk and over time spreads the data across the 3 disks OR do I have to do a backup/restore in order to configure a 3 drive parity system ?

Right now you would need to backup, destroy the current pool, recreate the pool using all the drives, copy your data back.

HOWEVER, in the next few years we may have zpool expansion. Google it, there is a thread here talking about it. But that will not exist for a while.

2) Instead of buying a 3rd 2TB drive if I buy a 4TB drive is there a way to have TrueNAS mirror the existing data on the 2x2TB mirror to the new 4TB drive and then I manually break the mirror and then manually configure the 2x2TB to be the mirror of the 4TB drive OR does this require a backup/restore OR is it not possible to mirror a single 4TB drive to 2x2TB drives?

Eh, I'll say yes but not the way you may be thinking of it. If you have a two drive mirror made of two 2TB drives and add a third drive as a mirror, you will have a 3 way mirror. You capacity at this moment will be limited to 2TB (minus formatting overhead). If you were to remove a 2TB drive and replace it with a second 4TB drive, you would still have 2TB because you still have a 2TB drive in the mirror. Now you remove the last 2TB drive and instantly your pool expands to 4TB. You can always go up in capacity but you can never go down.

As for if you could stripe two 2TB drives and then mirror that to a 4TB drive, I've never heard of that and I would not do it even if it were possible.

Hopefully I did not lie to you and that clears things up a bit.

 

[danb35]

is it not possible to mirror a single 4TB drive to 2x2TB drives?

No, this is not possible, and is unlikely to ever be.

HOWEVER, in the next few years we may have zpool expansion.

RAIDZ expansion still won't let you turn a stripe into RAIDZ.

 

[joeschmuck]

RAIDZ expansion still won't let you turn a stripe into RAIDZ.

From what I recall it was to add more drives to a RAIDZ configuration. Example: 4 drive RAIDZ1 to a 5 drive RAIDZ1. I am curious if it would allow a conversion from a RAIDZ1 to a RAIDZ2. When it actually come to the people, I'll learn about it then. I will be retired by then and have lots of time on my hands.

 

[danb35]

add more drives to a RAIDZ configuration. Example: 4 drive RAIDZ1 to a 5 drive RAIDZ1

Correct.

I am curious if it would allow a conversion from a RAIDZ1 to a RAIDZ2.

Not unless that's been added recently; it wasn't part of the scope initially. And with as hard as it was to get it out the door as it was, I'd be very surprised.

 

[Ericloewe]

ot unless that's been added recently; it wasn't part of the scope initially. And with as hard as it was to get it out the door as it was, I'd be very surprised.

It wasn't. It's actually fairly involved because it involves re-calculating and re-writing all the data. I don't think it could be done without traversing all block pointers to get the correct offsets for each block, which is not done at all for RAIDZ expansion, which operates on an LBA basis and little more.

 

[Davvo]

Yup, I also remember it not being in the scope of RAIDZ expansion.

 

[Etorix]

From what I recall it was to add more drives to a RAIDZ configuration. Example: 4 drive RAIDZ1 to a 5 drive RAIDZ1. I am curious if it would allow a conversion from a RAIDZ1 to a RAIDZ2.

No. As explained in the discussion thread (spanning from 2017…), expansion is done in the minimal way and existing data, which in your example was on 4-wide Z1 will remain in stripes of 3 data blocks and one parity block in the expanded 5-wide vdev; only data written after expansion will be striped in 4 data + 1 parity. Rewriting everything to add extra parity blocks is clearly not within the scope or within the plan.

Short take: Vdev expansion might be occasionally useful when it eventually lands—but it will not rescue or excuse bad pool design.

 

[csanii]

Right now you would need to backup, destroy the current pool, recreate the pool using all the drives, copy your data back.

HOWEVER, in the next few years we may have zpool expansion. Google it, there is a thread here talking about it. But that will not exist for a while.


Eh, I'll say yes but not the way you may be thinking of it. If you have a two drive mirror made of two 2TB drives and add a third drive as a mirror, you will have a 3 way mirror. You capacity at this moment will be limited to 2TB (minus formatting overhead). If you were to remove a 2TB drive and replace it with a second 4TB drive, you would still have 2TB because you still have a 2TB drive in the mirror. Now you remove the last 2TB drive and instantly your pool expands to 4TB. You can always go up in capacity but you can never go down.

As for if you could stripe two 2TB drives and then mirror that to a 4TB drive, I've never heard of that and I would not do it even if it were possible.

Hopefully I did not lie to you and that clears things

Right now you would need to backup, destroy the current pool, recreate the pool using all the drives, copy your data back.

HOWEVER, in the next few years we may have zpool expansion. Google it, there is a thread here talking about it. But that will not exist for a while.


Eh, I'll say yes but not the way you may be thinking of it. If you have a two drive mirror made of two 2TB drives and add a third drive as a mirror, you will have a 3 way mirror. You capacity at this moment will be limited to 2TB (minus formatting overhead). If you were to remove a 2TB drive and replace it with a second 4TB drive, you would still have 2TB because you still have a 2TB drive in the mirror. Now you remove the last 2TB drive and instantly your pool expands to 4TB. You can always go up in capacity but you can never go down.

As for if you could stripe two 2TB drives and then mirror that to a 4TB drive, I've never heard of that and I would not do it even if it were possible.

Hopefully I did not lie to you and that clears things up a bit.

Thanks for the info. The sequence you wrote makes sense. I was hoping for more auto-migration/zpool expansion capabilities. I bought a single 5TB external nonNAS drive ~5 years ago for about 66% of today's price and it was even cheaper than a single NAS 4TB drive today. Was hoping that storage doubled in size for same price but looks like price went up ....

 

[Davvo]

I bought a single 5TB external nonNAS drive ~5 years ago for about 66% of today's price and it was even cheaper than a single NAS 4TB drive today. Was hoping that storage doubled in size for same price but looks like price went up ....

You are comparing apples to oranges: non-nas HDDs are not designed for 24/7 usage for 3-5 years (and usually hold even longer), and more importantly are not CMR: SMR brings down the cost per space a lot.

Kick in the flash rise, the pandemic, and the increasing frictions with China... things start to add pretty fast.

 

[csanii]

You are comparing apples to oranges: non-nas HDDs are not designed for 24/7 usage for 3-5 years (and usually hold even longer), and more importantly are not CMR: SMR brings down the cost per space a lot.

Kick in the flash rise, the pandemic, and the increasing frictions with China... things start to add pretty fast.

Yes not the same type drive but even the same regular drive is 50% more than 5 years ago...very sad.....