Storage question

William A. Mahaffey III wam at
Wed Sep 9 15:17:15 UTC 2015

On 09/09/15 10:06, Steve O'Hara-Smith wrote:
> On Wed, 9 Sep 2015 09:47:00 -0453.75
> "William A. Mahaffey III" <wam at> wrote:
>> On 09/09/15 09:04, Steve O'Hara-Smith wrote:
>>> On Wed, 9 Sep 2015 08:23:54 -0453.75
>>> "William A. Mahaffey III" <wam at> wrote:
>>>> I like ZFS in principal (it's one of the things that attracted me to
>>>> FreeBSD about a year ago), but, as someone else noted, it seems to
>>>> require lots of RAM & possibly CPU for best effect. The MythTV box is
>>>> an AMD A4-5000, 1.5 GHz quad-core jaguar, w/ 16 GB of RAM, which isn't
>>> 	My house fileserver (erm NAS in modern speak) is a dual core
>>> Atom with 4GB. It manages a 4x2TB RAIDZ2 as well as a bunch of jails.
>>> According to top it has 2432M for ARC (3592M altogether is wired).
>>> Memory is tight but it's not swapping, and it doesn't no matter what
>>> the load. Switching to your spec would be a hefty upgrade and would
>>> almost certainly make things faster, but then most things can be made
>>> faster with an extra expenditure.
>>>> especially robusto by today's standards, so I am staying w/ UFS.
>>>> Someone
>>> 	If you have the opportunity then benchmark ZFS and see, if you
>>> can run it the benefits are great.
>> I am quite amenable to running ZFS, I just don't want to have to abandon
>> it & return to UFS if my system proves inadequate for the task, hence my
>> caution about it. If I go to ZFS, I (*think* I) use it for the whole
>> drives, except for swap (possibly), & slice it up into
>> 'partitions/slices/whatever' to do the install, right ? That was my
>> take-away from reading the online pages about it. Maybe I need to
>> rethink ....
> 	Yes that's essentially it - you assemble the raw storage you're
> going to use into a zpool from which the storage that backs the filesystems
> is drawn automatically. Once you have a zpool making a filesystem is very
> cheap. The filesystems share the pool, if you want to cap them you can but
> otherwise they're all limited by the pool. I've never filled a ZFS pool, I
> don't think I want to.

I have heard that filling your zpool is a *BAD* thing, but it can be for 
any FS, just maybe a bit worse for ZFS. I am going to study that option 
a bit more. The online docs all seem to show swap within the zpool as 
well, does that work OK, performance wise ? It would simplify 
installation, however I am planning to script that, so a bit of 'extra' 
effort for separate swap partitions is not an issue. I have always 
thought that separate swap partitions directly kernel managed were the 
best for swap performance if/when it gets down to that, no ?


	William A. Mahaffey III


	"The M1 Garand is without doubt the finest implement of war
	 ever devised by man."
                            -- Gen. George S. Patton Jr.

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