[PC-BSD Testing] Areas where FreeBSD needs work

Lars Noldan lars at w9zeb.org
Thu Dec 23 15:12:30 PST 2010

Hi Lars.

Thanks, I will get signed up for that list and resubmit.

On Dec 23, 2010 5:03 PM, "Lars Engels" <lars.engels at 0x20.net> wrote:
> 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
>> 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.
>> _______________________________________________
>> Testing mailing list
>> Testing at lists.pcbsd.org
>> http://lists.pcbsd.org/mailman/listinfo/testing
> 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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