Help to understand the disk thing with BTRFS

[PeteAsking]

Hi,

 

I upgraded to 6.9.0-beta35 yesterday. I read in the release notes on the forum about having to alter your disks to 1MiB-aligned.

 

Is this only for cache disks or any disk?

 

I have just 3 disks in a simple setup. They are all SSD. All filesystems were setup BTRFS on the old stable version over a year ago.

Parity - SSD - Samsung_SSD_860_EVO_1TB_S5B3NR0NB01634P - 1 TB
    976,762,552 KB (K=1024)
    MBR: 4KiB-aligned

Disk 1 - SSD -  ADATA_SU800_2K0820007524 - 512 GB  

    500,107,576 KB (K=1024)

    MBR: 4KiB-aligned

Disk 3 - SSD -  Samsung_SSD_970_EVO_500GB_S5H7NS0N971662A - 500 GB (nvme0n1)

    488,386,552 KB (K=1024)

    MBR: 4KiB-aligned

 

Am I supposed to move all the data off and delete them, format, and re-add them somehow to the array?

 

(I know SSD's are not supported but I always have used them because I need the speed for the VM's I use on Unraid. They do get written to a lot. I feel they are cheap enough to just replace if needed.)

[JorgeB]

1 hour ago, PeteAsking said:

Is this only for cache disks or any disk?

It's for any flash based device.

 

1 hour ago, PeteAsking said:

Am I supposed to move all the data off and delete them, format, and re-add them somehow to the array?

You don't "need" to use the new alignment, but it *should* improve performance and durability.

 

Note that to re-partition them you'd need to blow up the whole array and start over, can't just do it one device at a time since the devices will be a little smaller with the new layout.

 

 

[PeteAsking]

Hmm thats kind of impossible. How am I supposed to do this? Where does all my data go during the time I have to recreate the array. Seems rather drastic and inconvenient. I mean yes lets improve durability and performance. But how to complete this?

 

Is there no way to do one at a time? My cache drive is 1TB and the 2 disks in the array only 500-512GB. The cache drive can "become smaller" if that even makes sense because its already a lot bigger than the 2 disks.

Edited December 1, 2020 by PeteAsking

[PeteAsking]

I mean On /mnt/disk1 I have :

 

/mnt/disk1# ls
domains/  isos/  system/

 

 

and on disk 3 I have :

 

/mnt/disk3# ls
appdata/  domains/

 

Am I expected to just copy these folders somewhere... and then delete the array and recreate it and copy them back?

Or what?

[PeteAsking]

What about if I move all the data onto the 512GB disk and then unplug it and put it into my pc via USB then the remaingin 2 disks - the parity and the m.2 nvme disk just delete array and recreate and put all the stuff back on that one then later on add back the 512 disk when its all working off just 1 disk

 

Edited December 1, 2020 by PeteAsking

[PeteAsking]

Is this plan viable? What a nightmare.

[JorgeB]

2 hours ago, PeteAsking said:

How am I supposed to do this?

Backups?

 

Like mentioned you don't need to do this (though you'll run into trouble in the future if you need to replace one of the SSDs using a spare with the same size, it won't let you).

[PeteAsking]

Ok what about my plan I suggested above will that work?

Or are you saying the next time I replace a drive it will "fix itself" ?

[JorgeB]

11 hours ago, PeteAsking said:

Ok what about my plan I suggested above will that work?

As long as you backup the data you can do it, in fact you should already have backups.

 

11 hours ago, PeteAsking said:

Or are you saying the next time I replace a drive it will "fix itself" ?

No, I said you won't be able to replace a drive, unless you replace them all with larger capacity devices, starting with parity of course.

 

[PeteAsking]

Ok guess I have to start all over again with unraid then

[PeteAsking]

I stared all over again. Took a long time to be honest like 3 hours. Was not really fun and should really be a workaround to starting all over due to a bug. But there you go. It does seem like there are less writes to the drives now just from my short term looking so I guess it was ‘worth’ it. 

Edited December 6, 2020 by PeteAsking

[JorgeB]

6 hours ago, PeteAsking said:

Was not really fun and should really be a workaround to starting all over due to a bug.

It's not a bug, just a consequence of the new alignment, since the partition is now smaller it can be rebuild using the same size device.