[PC-BSD Testing] Areas where FreeBSD needs work

Lars Engels lars.engels at 0x20.net
Thu Dec 23 14:03:11 PST 2010


On Thu, Dec 23, 2010 at 11:30:25AM -0500, Lars R. Noldan wrote:
> On Dec.23 I shared the following the Dru in #PCBSD.  It was written by 
> my co-worker on Oct.10.  She requested that he post it here.  Since I 
> follow this list, and he doesn't I am going to post it here for him.
> 
> Thanks.
> Lars
> 
> FreeBSD needs work
> last modified on 2010-10-10 at 19:33 - keywords: freebsd zfs iscsi whining
> 
> Warning: This is not a post whining about Adobe Flash or how hard it is 
> to get my playstation controller to work in Quake.
> 
> This is, instead, a post whining about how hard it is to use ZFS and 
> iSCSI on FreeBSD. Recently I was tasked with building some 
> storage-related projects. The tools of choice involved FreeBSD sitting 
> on some hardware with a large collection of high-volume drives. These 
> drives were presented JBOD-style to the host OS, and a couple of them 
> were SSDs. The idea was to make one massive raidz2 zpool with a mirrored 
> ZIL on the SSDs. Then we could spin off zvols and pitch them via iSCSI 
> to our application and database servers.
> 
> Sound simple? It isn't. To get it working, we had to switch to 
> OpenSolaris. Which is a bit of a damn problem.
> 
> There were two really bad problems in FreeBSD that prevented us from 
> deploying our OS of choice to these systems.
> 
> Problem the first:
> ZFS on FreeBSD (at zpool version 13 as of this project) is only like 80% 
> there. What I mean by that is ZFS is friggin fantastic for your massive 
> desktop nerdmachine, or your creepy 8TB basement "media archive", or any 
> other low-traffic consumer-grade project you might want to undertake. 
> But when you start putting some load on it...
> 
> The biggest problem I had seemed to be caused by multiple read 
> operations during snapshot creation. If you took a snapshot while lots 
> of iSCSI (or NFS) (or local) access is going on, the zfs process gets 
> stuck with a wait state. What it boils down to is that you have to be 
> super careful to disable access while you're creating (or, in bad cases, 
> sending) snapshots off -- which completely wrecks the point of the damn 
> snapshot functionality.
> 
> Oh, and it would crash BSD too. Sometimes it would just eat all the RAM 
> and the machine would fall down.
> 
> Problem the second:
> iSCSI support in FreeBSD is abominable. I'm given to understand this is 
> because the main iSCSI dev in FreeBSD-land is possessed of insufficient 
> hardware to model high-performance workloads. If that's the case, we 
> need to get that man some damn hardware. Or convince Covad to update 
> their AoE stuff, since AoE is nicer anyway.
> 
> If the iSCSI traffic crossed subnets, performance would tank. If the 
> iSCSI targets were accessed from a non-FreeBSD initiator, performance 
> would tank. If a FreeBSD initiator accesses a non-FreeBSD target, 
> performance tanks. Are you seeing a pattern here? Best-practices 
> objections aside, it's clear that the dev has a handful of machines on a 
> dumb switch, and that's the test platform. As soon as you instantiate 
> some sophistication, the whole thing falls down. Again.
> How do we fix this?
> 
> I suppose I could devote some time to mastering the implementation 
> details of iSCSI and ZFS, then fix the stuff myself. That's not really 
> the best use of my time, however, and I'm not in a position to get paid 
> to do that sort of thing. But there are a few things anyone (myself 
> included) can do:
> test.
> 
>   * report bugs.
>   * provide stack traces and failure scenarios.
>   * whine constantly.
>   * provide testing hardware.
> 
> All of these are helpful, especially the constant whining. The problem 
> needs to be front-and-center, or it'll get de-prioritized in favor of 
> other (and in my opinion) less important problems. I don't give a crap 
> that your video card doesn't push hard enough to run EVE in FreeBSD. I 
> want the ZFS functionality that now only FreeBSD actively provides, and 
> I want the iSCSI functionality ZFS was designed to enable.
> 

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> Testing at lists.pcbsd.org
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Hi Lars,

I think that the PCBSD Testing mailing list might be the wrong list for
this problem.
Please send this issue to freebsd-fs at freebsd.org 

Cheers

Lars
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