Re: zfs: 9 vs current, and ZIL/L2ARC on ssd?

[Chavdar Ivanov <ci4ic4%gmail.com@localhost>]

On Thu, 11 Feb 2021 at 18:17, Greg Troxel <gdt%lexort.com@localhost> wrote:
>
>
> I am about to try to use zfs for the first time and have a few
> questions.
>
> I have a machine that is running NetBSD-9/amd64 with 2 cores, 8G of RAM,
> a single 1T SSD, with a smallish root/swap/usr, and about 870 GiB free
> intended for zfs.  I am heading for one po0l that is not raid at all.
>
> I'm not all that worried about transitions or stability; this is a build
> machine for packages, not particularly precious, and it being down for a
> week while I fix it is no big deal.
>
> I will likely pivot the machine to be xen dom0; I hope that doesn't
> matter much (other than 1 core only in the dom0).  Or I might use nvmm,
> or both.
>
> I might add a spinning disk later, either internal or USB.  (I realize
> that there, I probably want both ZIL and L2ARC on SSD.  I would rather
> move bits later than do things now to ease that, since I do not have an
> actual plan.)
>
> My questions are:
>
>   Is 9/current close enough to the same zfs code that it doesn't matter
>   which I run?  If I'm inclined to run current for other reasons, is
>   that a bad idea zfs-wise?
>
>   I understand that zfs has an intent log always, and that can be within
>   the pool, or one can add a ZIL device.  With the pool having one
>   device which is an SSD, I see no point in partitioning off part of
>   that SSD to be the ZIL.
>
>   I understand that zfs has ARC in RAM, and can have L2ARC on disk.
>   Given that the pool is on SSD, it seems pointless to split off some
>   for L2ARC.
>
> My expected answers are:
>
>   The code is basically the same and it doesn't really matter but
>   probably current has some bugfixes 9 doesn't.  There's no reason
>   current is scary becuase of zfs.

I have been using zfs on -current for quite some time; the system gets
upgraded 2-3 times a week, no problems so far.

>
>   There is no point in a ZIL on the same SSD as the pool.

Yes.

>
>   There is really no point in L2ARC on the same SSD as the pool.

Yes.

Even if you were to have more physical disks with a different setup,
l2arc and zil may not be useful; r/zfs is full with discussions on the
topic. 8GB physical memory is enough to run it, but you won't have
much left, my system has 20GB, I see at the moment:

Memory: 9235M Act, 4606M Inact, 19M Wired, 90M Exec, 13G File, 108M Free

But zfs on -current at least is quite usable; I only wonder when
OpenZFS 2.0 will be ported...

>
>
> Corrections/clues appreciated.



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