Less storage space with ZFS & 4k sectors enabled?

[wolf359]

Hi,

I'm in the process of setting up my FreeNAS system with FreeNAS 8.0.1 Beta 4 and as I am using Samsung HD204UI drives, I read a lot about 4k sectors here in the forum.
Most of the discussion is about a better performance, which is true. With 4k sectors enabled, I do have about 20% better read&write performance.

But I noticed that my raidz1 volume (4x 2TB) with 4k sectors is smaller than without 4k enabled!
To verify this I created the volume with 4k sectors via the web GUI and manually from command line. Both tests resulted in a significant small volume.

Reported in the GUI:

Without 4k sectors: 5.3TB

Code:

Filesystem 1K-blocks  Used      Avail Capacity  Mounted on
volume1    5732278193   31 5732278162     0%    /mnt/volume1

With 4k sectors 5.2TB

Code:

Filesystem 1K-blocks  Used      Avail Capacity  Mounted on
volume1    5567643281  162 5567643119     0%    /mnt/volume1

The numbers above are from freshly created volumes (WebGUI with default settings).

As we are speaking of TBs here, this difference is huge ~ 157 GB less storage with 4k sectors enabled!

Can anyone explain please what is going on here? And how to fix this?



P.S.: Yes, the HDDs are patched :D

 

[ClassicGOD]

I've noticed the same exact thing with 4 Seagate Barracuda Green 2TB drives. In my case when I forced 4k sectors the performance also went down from 250MB/s writes to 60MB/s - my guess is forcing 4K sectors causes some strange misalignment of the partitions on the drives.

 

[louisk]

It was my understanding from watching the mailing lists that the 4k support was intended for 4k disks. While it may work on other disks, I can't imagine it would be efficient. Are the disks you're using 4k? If not, I wouldn't force 4k formatting on them.

 

[ClassicGOD]

It was my understanding from watching the mailing lists that the 4k support was intended for 4k disks. While it may work on other disks, I can't imagine it would be efficient. Are the disks you're using 4k? If not, I wouldn't force 4k formatting on them.

Of course they are 4k drives. I'm talking about Seagate ST2000DL003 - SATAIII, 64MB cache, Advanced Format drives. Seagate markets them as the 4k drives that don't require 4k support from OS but still when using 4k sectors there shouldn't be any drop in performance (according to benchmarks online they should be 10-20% faster with 4k formatting). But when I force 4k sectors I get huge drop in performance and less space on my volume - it's definitely a bug in FreeNAS 8.0.1 Beta 4 and I hope it will be fixed in the future ;)

 

[wolf359]

As ClassicGODs drives, my Samsung HD204UI are Advanced Format Drives, too.