/usr/home vs /home

Da Rock freebsd-questions at herveybayaustralia.com.au
Sat Feb 18 13:52:57 UTC 2012


On 02/18/12 23:39, Matthew Seaman wrote:
> On 18/02/2012 11:36, Da Rock wrote:
>> If I may, can I ask a quick question: My main misgivings about ZFS have
>> been speed, ram use, and up till about a year ago or so relative 'youth'
>> (at least on FreeBSD). What would be the minimum ram you would use for a
>> high disk use? And what would be recommended to use for the caching? I
>> was thinking 8G ram and either a high quality usb/SD(/CF?) disk or a
>> sata II/III SSD for cache.
> Yes -- ZFS uses RAM heavily to improve performance.   I've a VM running
> ZFS with only 1GB which is pretty slow.   Mind you, a similar VM with
> UFS is also pretty slow.
>
> For an actual machine, about 4GB makes a reasonable ZFS system.  More is
> better though; 8GB is what I'd recommend.  ZFS speed is on the whole
> pretty reasonable.  It doesn't do small, randomized IO very effectively,
> so it's not ideal to run a database on.  Other than that, for a home
> e-mail / web /fileserver ZFS is just fine.
>
> I haven't tried SSDs or anything like that -- that's an optimization to
> improve latency when accessing lots of different files, and my usage
> doesn't really justify it.  Try it without before spending any money on
> SSDs.  It may well be good enough, but if it isn't then adding SSDs and
> making ZFS use them for ZIL or cache is pretty simple (and doesn't
> require any downtime.)
I was thinking along the lines of continuous heavy load of writing (some 
read) rather large files (5G+ would be average - multiple!) - does that 
warrant caching or is it only lots of smaller files? That and lots of 
~0.5G files (read mostly) is what defines the main load on the system.

I ask because I'm not 100% sure of what the caching is for. I had 
thought it was like the journal log for fast writing to be later written 
to the filesystem itself, but now I think I may be wrong in my 
judgement. It now sounds like a fast access for usual suspects.

Now you see how a terabyte and a half disk space can be used in a matter 
of hours :)


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