4K sectors on drive with 512b??

[alz]

Hi guys,
I built my first DIY NAS this week specs in my sig.
FreeNAS went on and was configured without issue except I did something silly late fri night and checked the "force 4K sectors" when creating my raidz1 volume without checking the data sheet for my ST33000651AS 3TB drives.
I just assumed that as they were new drives they would be 4k by default.
It turns out they have 512b sectors according to a pdf from seagate.
I have run

zpool set cachefile=/data/zfs/zpool.cache tank (change tank to your pool name)
zdb -U /data/zfs/zpool.cache | grep ashift

and it returned 12 so my question is should I rebuild my volume with the correct settings?
I have not noticed any problems yet other than rsync from my qnap is going extremely slowly(19mbs) but I put this down to the qnap cpu being maxxed out.
any feedback would be greatly appreciated as I have already dumped over 5tb and have still more data on tape that I am holding back on till I can figure this out.

 

[Milhouse]

I think it's better to go with 4K even if the drives are 512B - in a year or so if/when a drive fails, how likely is it that you will pick up another 512B drive instead of a 4K? Chances are it will be the latter, in which case you're all set. If you go with 512B now, you'll end up forcing a 4K drive to operate with 512B sectors which is likely to hurt performance, whereas the opposite doesn't appear to impact performance much, if at all.

 

[survive]

Hi alz,

I use 1TB Samsung drives which are also 512b drives, but I forced 4k sectors on purpose when I made my volume. I did this to sort of "future proof" it so if I ever decide to do the "swap each drive till they are all exchanged" trick to grow my volume I won't have trouble. There's also the problem of what happens when a drive fails and Samsung replaces it with something bigger that might be a 4k drive as well.

I didn't benchmark the system to extensively but the "dd" tests I did showed it cost me a few MB\s out of hundreds...seat of the pants measurements show no discernible loss of performance.

That said, I thought all 3TB drives were 4k sectored? You might want to confirm that because your setup might actually require it.

-Will

 

[alz]

Thanks for the input guys most appreciated!

@Millhouse
Thats exactly what I was hoping to hear, I am not concerned with a small performance hit my only concern was that the volume may be misaligned in some way that would lead to problems if I ever have to rebuild due to a failed drive.

@survive
Yep future proofing sounds like a decent enough reason to go the 4k route even if its does incur some small performance hit,
I also thought all 3tb drive were 4k standard thats why I checked the box initially but the next day when I went digging on the seagate site there is a pdf datasheet available off the main ST33000651AS support page that states

Configuration/Organisation
Heads/Discs 8/4
Bytes per Sector 512

This document only mentions the 2tb drive so I found the full technical manual for both 2&3 tb drive which confirms 512b sectors.
It was the lack of this info in plain sight that made me want to find out,

anyhoo thanks again for the quick resposes

 

[Milhouse]

...I went digging on the seagate site there is a pdf datasheet available off the main ST33000651AS support page that states

It is a 4K drive, but it uses SmartAlign (512B emulation) to keep non-4K aware operating systems happy.

This emulation business is starting to p'ss me off - since most (all?) new operating systems have support for native 4K, why not give users the option to disable the emulation that is only required by a legacy OS?