ZFS: alignment/boundary for partition type freebsd-zfs

O. Hartmann ohartmann at walstatt.org
Tue Dec 26 16:25:36 UTC 2017

Running recent CURRENT on most of our lab's boxes, I was in need to replace and restore a
ZFS RAIDZ pool. Doing so, I was in need to partition the disks I was about to replace.
Well, the drives in question are 4k block size drives with 512b emulation - as most of
them today. I've created the only and sole partiton on each 4 TB drive via the command

gpart create -s GPT adaX
gpart add -t freebsd-zfs -a 4k -l nameXX adaX

After doing this on all drives I was about to replace, something drove me to check on
the net and I found a lot of websites giving "advices", how to prepare large, modern
drives for ZFS. I think the GNOP trick is not necessary any more, but many blogs
recommend to perform

gpart add -t freebsd-zfs -b 1m -a 4k -l nameXX adaX

to put the partition boundary at the 1 Megabytes boundary. I didn't do that. My
partitions all start now at block 40.

My question is: will this have severe performance consequences or is that negligible?

Since most of those websites I found via "zfs freebsd alignement" are from years ago, I'm
a bit confused now an consideration performing all this days-taking resilvering process
let me loose some more hair as the usual "fallout" ...

Thanks in advance,


O. Hartmann

Ich widerspreche der Nutzung oder Übermittlung meiner Daten für
Werbezwecke oder für die Markt- oder Meinungsforschung (§ 28 Abs. 4 BDSG).
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