# is it possible to remove a SLOG device from ZFS on 7.2-current amd64



## winston879 (Mar 14, 2011)

I was wondering if it is safe (or even possible) to remove a log device from a zpool in FreeBSD.

I know opensolaris suffered a bug which made this not possible, and I've heard of it causing pools to become unbootable...

Also, does having a separate log device that isn't an SSD help performance at all?

Thanks for the input.


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## adri (Mar 14, 2011)

winston879 said:
			
		

> I was wondering if it is safe (or even possible) to remove a log device from a zpool in FreeBSD
> 
> I know opensolaris suffered a bug which made this not possible, and i've heard of it causing pools to become unbootable...
> 
> ...


Removing a log device is not possible with 7.2 release or 8.2 release.
You need to upgrade to 9.0 current or 8.2-stable with ZFS v28 patches applied.


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## phoenix (Mar 17, 2011)

winston879 said:
			
		

> I was wondering if it is safe (or even possible) to remove a log device from a zpool in FreeBSD.



Yes, it is possible ... *if* you are running a ZFSv19 or newer pool.

If you are using ZFSv18 or older (like ZFSv14 in FreeBSD 7.x or ZFSv15 in FreeBSD 8.x) then you cannot remove a log device, nor import a pool with a broken log device.



> Also, does having a separate log device that isn't an SSD help performance at all?



Yes, in some situations.  So long as the IOps rate for the log device is higher than the IOps rate of the pool, then you will get a benefit.  For example, if you build a raidz2 pool out of 5400 RPM drives, using a 15,000 RPM drive for the log device would help.

Of course, using a write-optimised, SLC-based SSD would be best.


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