freebsd-geom Digest, Vol 263, Issue 2

[Török Edwin]

On 2009-05-14 15:00, freebsd-geom-request at freebsd.org wrote:
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> Today's Topics:
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>    1. Re: compatibility with Linux software RAID? (Ivan Voras)
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>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 13 May 2009 14:56:37 +0200
> From: Ivan Voras <ivoras at freebsd.org>
> Subject: Re: compatibility with Linux software RAID?
> To: freebsd-geom at freebsd.org
> Message-ID: <gueg25$vbg$1 at ger.gmane.org>
> Content-Type: text/plain; charset="utf-8"
>
> Török Edwin wrote:
>   
>> Hi,
>>
>> Apologies if this has been answered before, but is there a way to access
>> (even if just read-only) RAID arrays created by Linux software raid
>> tools (mdadm)?
>>
>> I want to test the new superpages support in FreeBSD 7.2, and do some
>> performance comparisons with Linux, problem is all my data is on a
>> RAID10 array.
>>     
>
> RAID is not the only problem you have - how will you access the data?
> FreeBSD's ext2 file system driver isn't nearly as good for any kind of
> realistic performance testing - you'd probably need to test Linux with
> extX and FreeBSD with UFS2.
>   

I can test FreeBSD booted with superpages enabled vs FreeBSD booted
without superpages enabled.
You're right that comparing FreeBSD w/ Linux FS vs. Linux w/ Linux FS is
not fair.

I could copy the data to a temporary ramfs storage, and test from there
to eliminate filesystem differences.
(not taking the time needed to copy the data into account).

>   
>> Also if gmirror does support the above, is there a way to tell it to
>> treat the disks as readonly?
>>     
>
> Both gmirror and gstripe can work in a sort of "on-the-fly" mode,
> without actually committing any configuration to the drives (see the
> "create" command in both). In theory, you could use gmirror and gstripe
> with exactly the same parameters as you did in Linux to reconstitute
> your data. You'll also probably need gnop to align data before using
> gmirror and gstripe. Of course, only do this if you're completely sure
> what you're doing and know how RAID10 is physically implemented.
>   

Thanks, I'll do some experiments in a VM first, and if it all works I'll
move on to testing with the real drives.

Best regards,
--Edwin