Date: Thu, 09 May 2013 22:18:42 -0400 From: Benjamin Adams <benjamindadams@gmail.com> To: Jeremy Chadwick <jdc@koitsu.org> Cc: freebsd-stable@freebsd.org, Shane Ambler <FreeBSD@ShaneWare.Biz> Subject: Re: recommended memory for zfs Message-ID: <518C5902.5050909@gmail.com> In-Reply-To: <20130510020628.GA98750@icarus.home.lan> References: <518BA237.3030700@gmail.com> <518C450B.5070809@ShaneWare.Biz> <518C51AF.5050609@gmail.com> <20130510020628.GA98750@icarus.home.lan>
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On 05/09/2013 10:06 PM, Jeremy Chadwick wrote:
> On Thu, May 09, 2013 at 09:47:27PM -0400, Benjamin Adams wrote:
>> On 05/09/2013 08:53 PM, Shane Ambler wrote:
>>> On 09/05/2013 22:48, Benjamin Adams wrote:
>>>> Hello zfs question about memory.
>>>> I heard zfs is very ram hungry.
>>>> Service looking to run:
>>>> - nginx
>>>> - postgres
>>>> - php-fpm
>>>> - python
>>>>
>>>> I have a machine with two quad core cpus but only 4 G Memory
>>>>
>>>> I'm looking to buy more ram now.
>>>> What would be the recommend amount of memory for zfs across 6 drives on
>>>> this setup?
>>>>
>>> I believe I heard a calculation of 1GB cache per 1TB of disk. But
>>> basically zfs will use all free ram available if you access that
>>> much data from disk. You will want to set vfs.zfs.arc_max to allow
>>> enough ram for your apps to work in.
>>>
>>> If you consider the files for your website and the data you store
>>> you may find that you would never fill more than 500MB of cache.
>>>
>>> If you will be serving large media files that will easily use up
>>> the cache you could give them their own filesystem that only
>>> caches metadata - zfs set primarycache=metadata zroot/mediafiles
>>>
>>>
>> Thanks for all the replies Size of DB and HD's are:
>>
>> Current DB Size = 23 GB
>> HD sizes = (6) 500 GB drives
> Nobody is going to be able to give you a precise/accurate recommendation
> given the lack of detail provided, I'm sorry to say. What's the RES
> size of nginx (all processes combined)? What's the RES size of
> postgres (same)? Do you have PHP scripts that "run amok" for long
> periods of time and take up lots of RAM? Same with python? How many
> concurrent visitors and what sort of content are you hosting? Do you
> maintain/write your own PHP/Python code or are you using some crap like
> Wordpress?
>
> This is just a **small** list of questions -- and what may come as a
> shock is that I do not expect you to provide answers to any of them.
> They are questions that you should, for yourself, attempt to answer and
> work out what you need from there ("teach a man to fish" and all that).
>
> The advice of "1GB of RAM per 1TB of disk space" is absolute nonsense on
> numerous levels -- whoever gave this advice to Shane either has no
> understanding of how filesystems/ZFS works, or does but chose to
> simplify to the point where they're providing half-ass information.
> There is no direct, or even indirect, correlation between disk capacity
> and ZFS ARC size -- what matter is your "working set" (to quote Tom).
> You need to have some idea of how much disk I/O you're doing, and what
> type of I/O (sequential or random).
>
> If you want my general advice, Benjamin, it's this: get yourself a
> system with *minimum* 8GB of RAM but has the physical possibility of
> supporting more (and only add more RAM when/if you know you need it); do
> not bother with ZFS on a system with 4GB. Run amd64, not i386 (I don't
> recommend bothering with ZFS on i386 -- I am not going to get into a
> discussion about this either). Run stable/9, not 9.1-RELEASE. Avoid
> compression and dedup. And test disk failures as well (don't get caught
> with your pants down later).
>
> The above advice comes from someone who did hosting (web/ssh/etc.) for
> almost 20 years with KISS principle applied at all levels. YMMV though,
> depending on what all you're doing/what you truly need.
>
> Good luck.
>
Jeremy,
Was just see if I should just get raid controller and more ram down the
road.
List of priorities.
Main thing is I move from BSD when 9.0 came out. Was looking to see if
zfs is included in the installer. Now.
Sum up:
upgrade ram to 16GB (not 64 like plained)
and raid controller that supports level 5.
Thanks
Ben
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