[zfs-discuss] system hangs running find on .zfs subdirectory

Matthew Robbetts wingfeathera at gmail.com
Mon Apr 30 09:28:23 EDT 2012

On 30 Apr 2012, at 14:12, ray wrote:

> I'm starting to wonder if there's isn't an inherent flaw with ZFS
> design on PC systems, in that ZFS seems to require an inordinate
> amount of RAM in order to work reliably.

Well, yes and no. ZoL is not ready yet, in that the developers are still working on integrating ZFS's various memory and caching behaviours cleanly into the Linux kernel. At the moment there are outstanding issues with memory management such that you cannot use all of your physical memory for ZFS (as you will be able to in the end), because it will crash, deadlock, or otherwise misbehave. Again, this is simply because the Linux integration work isn't complete.

> I've had zfs-fuse running fine on a 2GB 32-bit Debian/Ubuntu system,
> but recently have been trying zfsonlinux because it is in active
> development and now supports .zfs/snapshot access (which zfs-fuse
> doesn't have).   ZFS Version 0.6.0-rc8 wouldn't even survive the first
> set of regression tests.  So I upgraded to a 64-bit Ubuntu.  On the 64
> bit system passed the regression tests fine, but got a kernel oops
> when I started playing with looking at snapshots.

Again, ZoL isn't finished yet. Hopefully within the next few months, these sorts of issues will be behind us. ZoL is making great strides at the moment. It is very unfortunate that you're getting issues with such fundamental usage, since many people are lucky enough to be using ZoL all the time with good behaviour. Have you opened a bug on the tracker for your oops? Responses there tend to be given pretty quickly. Also, as I understand it, several oopses and panics are known about and workarounds are in place pending proper fixes. Some problems are even caused by particular kernel configurations. So, it may be that you can alleviate your issue immediately.

> It is absurd for a
> desktop PC to require several GB's of ram just to support a filesystem.

I don't know how you came to this idea. ZFS isn't just "a filesystem". If all you want is a way to store files on a disk, use Ext3. It's memory requirements are small. ZFS has many more features, features which simply require things to be remembered. So, the large memory requirements are not due to inefficiency in ZFS's design, they are due to the fact that ZFS provides inherently memory-hungry features (and the requirements of ZFS actually change as you enable or disable specific optional stuff, like dedupe and compression). If you don't need these features, there's a plethora of filesystems that are tailored for other uses. If you do need them, then frankly, suck it up. There is no way to get these features in any filesystem without providing the memory.

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