Just curious: replacing older drive with '4k enabled' drive?

[RvdKraats]

Hi Guys,

just something that popped into my mind: suppose i want to expand my vdev capacity by replacing the old drives with newer, bigger capacity drives one-by-one, until all of them are the bigger capacity disks.

Is it possible to put a 'replacement disk' in 4k sector-mode, and then resilver? Or would that introduce problems in the overall vdev disk structure? A slowdown would be acceptable, as in then end all disks would be replaced by the newer disks.

 

[paleoN]

Is it possible to put a 'replacement disk' in 4k sector-mode, and then resilver?

No, it isn't possible. "4k sector-mode" can only be set a pool creation, it's set at the pool level, and can't be changed afterwards. You would need to backup your pool, delete the pool and recreate the pool with the proper ashift.

 

[RvdKraats]

Hmmm...allright, thanks for the info paleoN....i'm not sure if it's worth the trouble recreating the pool in terms of performance gains (my setup's primarily used to deliver 720p video / mp3's to 2 simultaneous users at most), so if i'm not able to temporarily store my data on another NAS i'll probably leave it like this (unless the performance gains would be HUGE)...

P.S. my setup is a HP XW4600, 8GB mem, Core 2 Quad 2.6 GHz, RAID-Z2 (4x 1TB).

 

[paleoN]

(unless the performance gains would be HUGE)...

The write performance gains are significant. Whether or not it's worth it to you I couldn't say. Given that all new HD's are 4k native I wouldn't want to carry this pool around forever.

 

[RvdKraats]

Hmmmm...i took the time to check the 1TB drives yesterday, and apparently these models don't support 4k mode :(
Oh well, saves me some hassle for now... ;)

 

[paleoN]

Hmmmm...i took the time to check the 1TB drives yesterday, and apparently these models don't support 4k mode :(

There is little to no performance hit, in an optimal pool configuration, with 512b drives set to 4096 sector size unlike the reverse. The 512b drives simply do their reads and writes in multiples of 8.

If it's more convenient you can wait. You are just going to have even more data then.

 

[RvdKraats]

Ah, is see...so forcing 4k mode is perfectly valid? My setup won't grow much beyond 4x2TB or 4x3TB in RAIDZ2, so if i need to copy data over to rebuild my zpool it won't be that much of a hassle, but still, nice to know i can already prepare for future 4k drives :)

Thanks!