hello everybody !

 

i have a pool cache with 2 NVME SSD of 1 Tbytes (so 1T size in RAID 1).

I would like to extend it to 2T by adding a 1T sata SSD 2.5 disk (so less performance)

- could it be a problem ?

- if the thrid HDD has 980Gbytes available and the 2 other 1Terabytes, what happen ?

 

regards

You can do that and assuming btrfs, you would have 2TB usable in raid1, but the pool speed would be limited by the HDD, always for rights, and around half the time for reads.

Thanks @JorgeB,

a question: why around half  the time on the HDD as there are 3 disks ?

1 hour ago, nunu22 said:

why around half  the time on the HDD as there are 3 disks ?

The data will be mirrored on the two SSD and the disk, for reads, btrfs uses one mirror or the other, based on even or odd process number, so some will come from the disk, others from the SSDs.

I thought you had 2 x 1TB and intended to add 1 x 1TB?    If do the usable space would end up as about 1.5TB as all data must exist on at least two drives with btrfs RAID1 profile.   You would only have 2TB available if the extra drive was a 2TB one.

@itimpi

you're right. I will have two 1Tbytes NVME disk + a third one.

- So if i add a 1TByte, i will have a 1.5T (in fact, it is logic ....)

- But if i add a 2 Tbytes SSD, Pool will automatically merge the two 1Tbytes NVME into One of 2Tbytes and Mirror it on the 2Tbytes SATA ?

 

57 minutes ago, nunu22 said:

But if i add a 2 Tbytes SSD, Pool will automatically merge the two 1Tbytes NVME into One of 2Tbytes and Mirror it on the 2Tbytes SATA

Yes.    You can use the BTRFS Calculator to work out the available space with mixes of different size disks and different btrfs profiles.

 

thanks.

so, i suppose that during operation, cache data won't be lost ?!  I just need to set pool size to 3 devices and add the device, and that it's ? should i stop docker services during the cache build ?

19 hours ago, itimpi said:

I thought you had 2 x 1TB and intended to add 1 x 1TB?

Sorry, misread, in that case it will be 1.5T total as mentioned.

12 hours ago, nunu22 said:

so, i suppose that during operation, cache data won't be lost ?!

As long as the pool is raid1 you can add an extra device, in doubt post the diagnostics.

with the calculator, i see that in raid5 with an additionnal 1TBytes disk, i would have 2T available

That is correct, but btrfs raid5 is still considered experimental, I would recommend zfs raidz instead.

Thanks a lot.

I think i will stay on RAID 1 + btrfs as it is straight forward. With 2T for the cacheit will be enough.

Thanks for the support !
regards

Hello !
back on the subject :
I have added the 2T SSD, and here the result :

It seems that USED and FREE representation are not correct.
Size is 2T, but if add USED and FREE space, i don't have my 2T of space ?!
mayeb i'm wrong ?

 

What's the pool configured as? RAID1?

 

BTRFS can technically work with different sized drives but will lead to quirks like that not really knowing what space it has available to work with. Also tends to be less reliable. 

 

Did you click on Cache and do a Balance?

yes it is RAID1
it seems taht balance is not necessary ?

36 minutes ago, nunu22 said:

It seems that USED and FREE representation are not correct.

That a btrfs issue when used with an odd number of devices, but you will be able to use the 2TB, and the stats will get closer to real as the pool gets filled up.

Thanks.
As i'm using mover plugin (with % for disk used from moving data from cache), i guess it will based on false free space estimation ?

It will depend on what is uses for the check, I would guess df or similar, and in that case yes, it will be based on what you see.