Re: FYIO: A rant about btrfs

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2015-09-17 10:52, Aneurin Price wrote:
> On 16 September 2015 at 20:21, Austin S Hemmelgarn <ahferroin7@gmail.com> wrote:
>> ZFS has been around for much longer, it's been mature and feature complete for more than a decade, and has had a long time to improve performance wise.  It is important to note though, that on low-end hardware, BTRFS can (and often does in my experience) perform better than ZFS, because ZFS is a serious resource hog (I have yet to see a stable ZFS deployment with less than 16G of RAM, even with all the fancy features turned off).
>
> If you have a real example of ZFS becoming unstable with, say, 4 or
> 8GB of memory, that doesn't involve attempting deduplication (which I
> guess is what you mean by 'all the fancy features') on a many-TB pool,
> I'd be interested to hear about it. (Psychic debugger says 'possibly
> somebody trying to use a large L2ARC on a pool with many/large zvols')
>
> My home fileserver has been running zfs for about 5 years, on a system
> maxed out at 4GB RAM. Currently up to ~9TB of data. The only stability
> problems I ever had were towards the beginning when I was using
> zfs-fuse because zfsonlinux wasn't ready then, *and* I was trying out
> deduplication.
>
> I have a couple of work machines with 2GB RAM and pools currently
> around 2.5TB full; no problems with these either in the couple of
> years they've been in use, though granted these are lightly loaded
> machines since what they mostly do is receive backup streams.
>
> Bear in mind that these are Linux machines, and zfsonlinux's memory
> management is known to be inferior to ZFS on Solaris and FreeBSD
> (because it does not integrate with the page cache and instead grabs a
> [configurable] chunk of memory, and doesn't always do a great job of
> dropping it in response to memory pressure).
>
I should qualify this further, in particular I meant using ZFS on Linux 
(not *BSD, they did an amazing job WRT stability), and actually taking 
advantage of the volume-management (ie, not just storing files on it, 
but also using zvols).  In essence, A better way to put it is that I've 
never seen a truly stable system using zfsonlinux with less than 16G or 
RAM which is using it for volume-management as well as file storage.


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