HDD Question for the Gurus

[Mr_N]

So I currently have a pool in my FreeNAS with 2 vdev's of 6 HDD's which are all 4TB SAS 512n drives.

With the bigger drives being 4Kn or 512e these days I was wondering if there are going to be any problems adding a vdev of 4Kn drives when I next increase storage?

Or should I keep using 512e Drives?

 

[joeschmuck]

I'm not positive, haven't look into it in a while but I believe the 4K drives still offer 512 byte emulation. You do ask an interesting question. So are your drives currently writing 4k blocks, meaning was the pool created in 4k sectors? If they are writing in 4k blocks then it should be blind to the system when you add 4k drives, it should work slightly better I'd think. Which new drives are you looking at?

 

[Mr_N]

nah given they are native 512 I doubt the pool is doing 4K unless that was the default when i made it...
can i get that info from a CLI cmd?

 

[Stux]

You can, I forget the details but you're looking for the ashift of the pool. You want 12 not 9.

 

[joeschmuck]

When I created my pool many years ago I ensured I had setup 4k on the proper boundary and I have an ashift value of 12. Here is how you check it.

Code:

zdb -U /data/zfs/zpool.cache | grep ashift

 

[Robert Trevellyan]

Or just zpool get ashift.

 

[joeschmuck]

Or just zpool get ashift.

My system returns the following error message using this command:

Code:

bad property list: invalid property 'ashift'

 

[Arwen]

Or just zpool get ashift.

This does not work on the current FreeNAS 9.x.

I do use that with ZFS on Linux. It's possible it was a ZOL feature that has not yet been ported
to the rest of the OpenZFS projects. Or that FreeNAS 9.x is a little behind.

 

[Mr_N]

So my pool reports ashift of 12

Does this mean it would be better to add 4Kn drives?

 

[Stux]

It means your pool operates in multiples of 4KiB.

If you had 9, then it would be operating in multiples of 512 bytes (0.5KiB), and that would not work well with 4K drives... since it'd be writing partial blocks continuously.

So, 4K drives are fine, and frankly, more modern.

 

[Mr_N]

sounds good :)

 

[Robert Trevellyan]

Does this mean it would be better to add 4Kn drives?

It means there will be no performance penalty when using advanced format a.k.a. AF drives, i.e. drives with 4K physical sectors. Older drives with 512B sectors will work fine too.