Need some advise on building a raidz2 and expand it later

[b7842]

I have 2 old 4TB WD Red which have ~6TB data.
My plan is to build a 8 bay raidz2. 4TB * 8
I have just bought the new hardware as following:
G4400
Asrock c236 wsi
16GB Kingston ecc ram * 2
SilverStone DS380
Corsair SFX450

My question is that Can I build the raidz2 with 4 Brand new 4TB Red first? Then, migrate 6TB data to it.
After that, expand it with another 4TB *4? Thank you

 

[b7842]

After reading 10 more posts, I found that it is not able to change the zpool once it is created.
If I want to build a 8 bay with raidz2, i should create it with 8 disks by one time.

 

[mattbbpl]

After reading 10 more posts, I found that it is not able to change the zpool once it is created.
If I want to build a 8 bay with raidz2, i should create it with 8 disks by one time.

You are absolutely correct.

 

[melloa]

Can he do a 2nd vdev later and add to the pool?

@b7842, read this: https://forums.freenas.org/index.ph...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

 

[b7842]

You are absolutely correct.

I found a raidz calc here
If i want to build a 8 bay raidz, i cannot use the old 4TB Red.
I need to buy 8 brand new WD 4TB red.
Am i correct?
Then, I havc 10 4TB WD red.
How can i make use the extra 2 old 4TB red? Thanks


http://wintelguy.com/raidcalc.pl
Results:
Total usable storage capacity (TB): 24.00 *
RAID type: RAID-Z2 (double parity with variable stripe width)
Number of RAID groups: 1
Number of drives per RAID group: 8
Total number of drives: 8
Drive capacity (GB): 4000
Capacity of a single RAID group (GB): 24000
Space efficiency: 0.75 (75%)
Fault tolerance: 2 disk drives per RAID group
Minimum number of disks drives per RAID-Z2 group: 4
Single drive cost: 1000
Cost per TB usable: 333.33
Total cost: 8000.00

 

[mattbbpl]

Can he do a 2nd vdev later and add to the pool?

@b7842, read this: https://forums.freenas.org/index.ph...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

Of course.

 

[mattbbpl]

If i want to build a 8 bay raidz, i cannot use the old 4TB Red.
I need to buy 8 brand new WD 4TB red.
Am i correct?

Sorry, you lost me (it's been a long evening). Why can't you use the older drives?

 

[Stux]

You can play musical chairs with partitions etc.

So basically, buy 6 extra disks... partition 4 of the disks into two slices each. Make a raidz2 with those 8 slices. Then copy your data to the slices, then replace the slices with your other drives and then the originally sliced drives.

If you're interested we can go into the specifics.

 

[b7842]

Sorry, you lost me (it's been a long evening). Why can't you use the older drives?

You can play musical chairs with partitions etc.

So basically, buy 6 extra disks... partition 4 of the disks into two slices each. Make a raidz2 with those 8 slices. Then copy your data to the slices, then replace the slices with your other drives and then the originally sliced drives.

If you're interested we can go into the specifics.

For my understanding, I can add another virtual device after the zpool created.
e.g.
At the beginning, i used 4 hard disks to build virtual device A.
Then, i run raidz2 in virtual device A.
Later, i buy 4 more hard disks.
At this moment, I cannot add the brand new 4 hard disks to the virtual device A.
I need to build virtual device B and add it to the zpool.
Am i correct?

My concern is that If i do not build the 8 bay in one time.
The efficiency will be low.

 

[Stux]

you buy the 4 drives. You split them 2 ways each. Then you make an 8 way raidz2 on 4 drives.

Then you copy the 2 drives worth of data to this new pool (replicate).

Then you replace the slices with whole drives until you end up with an 8 way raidz2 made out of 8 4TB disks, instead of 8 2TB slices.

 

[b7842]

you buy the 4 drives. You split them 2 ways each. Then you make an 8 way raidz2 on 4 drives.

Then you copy the 2 drives worth of data to this new pool (replicate).

Then you replace the slices with whole drives until you end up with an 8 way raidz2 made out of 8 4TB disks, instead of 8 2TB slices.

Thanks i will do an experiment tonight by vmware.

 

[danb35]

After reading 10 more posts, I found that it is not able to change the zpool once it is created.

I'm not sure what you read, but you found incorrectly. It is absolutely possible to change a pool once it's created. You can create a four-disk RAIDZ2 pool, and add another four disks in RAIDZ2 later, for example. This would give you one pool consisting of two vdevs, each with four disks in RAIDZ2. What you can't do is turn a four-disk RAIDZ2 vdev into an eight-disk RAIDZ2 vdev.

 

[Pitfrr]

Just an other though about backups:

if your concern is maximising the drives used (i.e. use your 2 old drives in your setup), I understand that you would like to find a way to use all your drives at once (and that might prove to be difficult since the 2 old drives already have data on it).

But in your initial message there is something that is not mentionned: backups?

Do you have backups of the data on these 2 old drives?
If yes then you don't have any problem using all the drives at once (then you need only to get 6 drives).
If not then you should consider backups and you might just use your 2 old drives as it (and therefore you'll have to get 8 drives).

 

[b7842]

I'm not sure what you read, but you found incorrectly. It is absolutely possible to change a pool once it's created. You can create a four-disk RAIDZ2 pool, and add another four disks in RAIDZ2 later, for example. This would give you one pool consisting of two vdevs, each with four disks in RAIDZ2. What you can't do is turn a four-disk RAIDZ2 vdev into an eight-disk RAIDZ2 vdev.

My concern is that
if I build it in two times, the space efficiency will be 50%.

Results:
Total usable storage capacity (TB): 8.00 *
RAID type: RAID-Z2 (double parity with variable stripe width)
Number of RAID groups: 1
Number of drives per RAID group: 4
Total number of drives: 4
Drive capacity (GB): 4000
Capacity of a single RAID group (GB): 8000
Space efficiency: 0.5 (50%)
Fault tolerance: 2 disk drives per RAID group
Minimum number of disks drives per RAID-Z2 group: 4
Single drive cost: 1100
Cost per TB usable: 550.00
Total cost: 4400.00
==========================================
If I build it in one time, the space efficiency will be 75%.
Results:
Total usable storage capacity (TB): 24.00 *
RAID type: RAID-Z2 (double parity with variable stripe width)
Number of RAID groups: 1
Number of drives per RAID group: 8
Total number of drives: 8
Drive capacity (GB): 4000
Capacity of a single RAID group (GB): 24000
Space efficiency: 0.75 (75%)
Fault tolerance: 2 disk drives per RAID group
Minimum number of disks drives per RAID-Z2 group: 4
Single drive cost: 1100
Cost per TB usable: 366.67
Total cost: 8800.00

 

[b7842]

Just an other though about backups:

if your concern is maximising the drives used (i.e. use your 2 old drives in your setup), I understand that you would like to find a way to use all your drives at once (and that might prove to be difficult since the 2 old drives already have data on it).

But in your initial message there is something that is not mentionned: backups?

Do you have backups of the data on these 2 old drives?
If yes then you don't have any problem using all the drives at once (then you need only to get 6 drives).
If not then you should consider backups and you might just use your 2 old drives as it (and therefore you'll have to get 8 drives).

I guess i will buy 8 new drives and use rsync to copy the data to the new pool
For the old drive, I will save it for spare

 

[danb35]

if I build it in two times, the space efficiency will be 50%.

More accurately, if you build a four-disk RAIDZ2 vdev, the space efficiency will be 50%. This is true whether your pool consists of one, two, or n such vdevs.