geom_raid5 inclusion in HEAD?

John Nielsen lists at
Tue Nov 6 11:53:17 PST 2007

[repost with the correct from: address]
Quoting "" <bsd at>:
> I was wondering if and when the excellent geom_raid5 module created 
> by Arne Wörner would be committed to HEAD or releng_7. Right now 
> there's gvinum with RAID5 support and geom_raid3. The latter is nice 
> but only works with a 'strange' number of disks (3,5,9,17,33, etc) 
> and has the disadvantages associated with RAID3 (no parallel access; 
> all disks are involved in one single write operation), while gvinum 
> offers poor RAID5 write performance (~20MB/s in my testings).
> geom_raid5, on the other hand, offers excellent performance due to 
> write combining, that allows 2-phase requests to be converted into 
> 1-phase requests. This is achieved by waiting for contiguous requests 
> and splitting those into the 'full stripe', meaning: stripesize * ( 
> number_of_disks - 1). This way, no parity information has to be read 
> from any disk since all required data is already in memory. In normal 
> english this means excellent sequential performance. In my own 
> testings i have achieved over 400MB/s of RAID5 write performance 
> using a simple "dd if=/dev/zero of=/dev/raid5/data bs=1m" of at least 
> 10GB worth of data. raidtest benchmarks show that geom_raid5 scales 
> nicely with the number of disks, though ofcourse RAID5's weak point 
> is random write.
> Considering this project has been around for quite a while, and 
> sister project FreeNAS has been using it for more than a year in 
> their official (stable) branch, i think it should become available in 
> the official FreeBSD distribution as well. I don't know who decides 
> on this, but i would like to get a discussion going on this matter.

I would like to see this get wider testing and eventually be included 
as well. A few questions (some of which I know the answer to but would 
like to have you field for the list):

Where can I get/test/review the code?

Is there still any focus on the "previous" generation code or is "TNG" 
where everything is happening now? Which generation are you talking 
about above?

Does the code in the FreeBSD perforce repository represent the latest 
improvements? Which generation?

How much and what kinds of testing has it already received? What is the 
relationship between the FreeNAS project and the geom_raid5 
developer(s)? What version(s) of the code is/are in FreeNAS? Has the 
FreeNAS project or anyone else done any (preferrably thorough and 
repeatable) testing for correctness, stability and performance? Are the 
methods and/or results publicly available?

Just who is (/are) the developer(s) behind this code?

Where can I get more information? Can the information on your blog be 
considered authoritative?

What is the status of the code? Are there any known outstanding issues 
or poorly tested functionality/configurations?

Are there any threads on the freebsd-geom or other mailing lists that 
would be enlightening? Has a call for testing and/or code review been 
made on that list recently?

Thanks. :)


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