[SOLVED] Made ZFS raid with ashift=12 on 512n Drives, will this effect performance?

User9 · 09-04-2017, 02:54 PM

I created a pair of striped mirrors (raid-10) with this . . .

Code:

>zpool create -f -o ashift=12 -o cachefile=/etc/zfs/zpool.cache -O normalization=formD -O atime=off
-m /mnt/zfs_pool zfs_pool mirror /dev/disk/id1 /dev/disk/id2 mirror /dev/disk/id3 /dev/disk/id4

As you can see I used ashift=12 even though my disks are 512n(4x WD Re4 WD1003FBYZ 1TB 64MB Cache) so when a drive gets replaced I can use 512e or true 4Kn Hard Disks

Will this slow my raid ? and/or Will this effect the raid in anyway ?

User9 · 09-05-2017, 09:49 PM

Looks like I've finally found my answer . . .
http://open-zfs.org/wiki/Hardware#Hard_drives

Quote:

As of 2014, there are still 512-byte and 4096-byte drives on the market, but they are known to properly identify themselves unless behind a USB to SATA controller. Replacing a 512-byte sector drive with a 4096-byte sector drives in a vdev created with 512-byte sector drives will adversely affect performance. Replacing a 4096-byte sector drive with a 512-byte sector drive will have no negative effect on performance.

Looking at this information it seems that if a raid created for 4Kn drives(ashift=12)
won't take a performance hit when a 512n drive is put in the raid then I should be okay as
the new 512n drive would inherit ashift=12 from the raid. So I'm going to assume it should
be fine, you just lose a little space.

jefro · 09-06-2017, 02:50 PM

Thanks for the update and solution.

User9 · 01-29-2018, 07:28 PM

I would like to update this again as I have recently got a new set of drives that are 512e these disks are on average 30 MB/s faster per a disk. This is with all the same stats 64MB Cache and 7200RPM. So one would think that if you had a set of these disks going at avg. 161.68 MB/sec and replaced one with a 512n going at 131.48 MB/sec it would slow the whole raid down.
But it still holds true that formatting with ashift=12 is the better option in this situation. Or any situation for that matter unless you have 512n disks and want the most space(over performance) and don't ever plan on using 4Kn drives in the raid.