Force 4096 bytes sector size?

[Norlig]

Hi,

first time setting up my Freenas, I was wondering if I should enable Force 4096 Bytes sector size?

I am going for a ZFS RAID5 equivalent. 4x2TB

thanks

 

[cyberjock]

It's like this. You can't change it later for that vdev. Based on testing from the end of last year choosing 4k sector size on disks that don't have 4k sector causes a very slight performance drop. But if your disks are 4k sector and they end up with an ashift=9(512-byte sectors for ZFS) there can be a major performance penalty.

tl;dr- I always choose 4k sector size except for SSDs.

 

[Norlig]

my disks are Seagate Barracuda's. I found out they do have 4096 bytes per sector. how do I know if they "end up with an ashift=9" ?

 

[cyberjock]

zdb -C yourpoolname | grep ashift

 

[cyberjock]

If your disks are 4k sector size and you do NOT end up with an ashift=12 using the default configuration with 9.1 RC then there is a bug. It's discussed slightly in http://forums.freenas.org/threads/zfs-4k-disk-alignment-gui.13816/#post-65420 and ticket https://support.freenas.org/ticket/2404

If you have this issue please post back so we can see what is going wrong.

 

[Norlig]

I got Ashift: 12

I use 8.3.1 P2 though, should I use 9.1 you say?

 

[cyberjock]

It's only an RC, so it may have bugs. If you are using 8.3.1-p2 stick with it.

 

[Sir.Robin]

Oyh... I have ashift 12 on my secondary, but 9 on my primary. All disks are a bit older ones, so 512 bytes sector size.

BUT i have a question :)

If i open volume manager on my 8.3.1 P2 box and choose my volume (wich is ashift 9) under the "Volume to extend"

I can choose "Force 4096 bytes sector size" and press "Extend Volume"

What happens then?

 

[paleoN]

What happens then?

The newly made vdev is created, via gnop, with an ashift=12. The first vdev's ashift will still be 9.

 

[cyberjock]

The only way to get your vdev to an ashift=12 is to destroy the zpool and recreate it :(

 

[Sir.Robin]

Crap... But no biggie yet for me. :)

 

[cyberjock]

Check out my sig.. "RAID5 is dead" and has been for years.