Date: Thu, 6 Sep 2001 15:28:41 +0930 From: Greg Lehey <grog@FreeBSD.org> To: "Chad R. Larson" <chad@DCFinc.com> Cc: Jason DiCioccio <geniusj@bluenugget.net>, FreeBSD-Stable <stable@FreeBSD.ORG> Subject: Re: CCD vs VINUM [was Re: RAID5] Message-ID: <20010906152841.K24413@wantadilla.lemis.com> In-Reply-To: <20010905142751.B6345@freeway.dcfinc.com>; from chad@DCFinc.com on Wed, Sep 05, 2001 at 02:27:51PM -0700 References: <20010903142145.K10812-100000@topperwein.dyndns.org> <200109041749.KAA12474@mina.soco.agilent.com> <20010905014103.A70986@bluenugget.net> <20010905142751.B6345@freeway.dcfinc.com>
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On Wednesday, 5 September 2001 at 14:27:51 -0700, Chad R. Larson wrote:
> On Wed, Sep 05, 2001 at 01:41:03AM -0700, Jason DiCioccio wrote:
>> vinum, IMHO, has the BEST manpage I've ever seen out of an open source
>> product.
>>
>> It has a ton of examples and explains things very well although it's
>> quite lengthy. Therefore i'm not sure what the issue was with setting
>> up the mirror.
>
> Is there a pointer somewhere to a comparison between ccd and vinum?
Not that I know of. As far as I can tell:
1. CCD only provides concatenation, striping and mirroring. I don't
expect it to perform significantly differently from Vinum in this
area.
2. You can argue the point, but I find Vinum configuration more
understandable.
3. CCD doesn't save the configuration information on the disk. Lose
the config file and your disks are toast. With Vinum, on the
other hand, you can remove the drives, change the IDs, replace
them and restart with no further problems.
4. Vinum notes the state of each component in the saved
configuration. If one component of a mirror goes down and the
other continues to be updated, it will still know the fact after a
reboot, thus ensuring data integrity. CCD doesn't save the state
anywhere.
5. (I'm not sure if this is still the case, but I haven't heard of
any change). If half a CCD mirror goes down, you need to take the
ccd down and reconfigure, maybe reboot, before you can use the
other half. With Vinum, you can carry on using the volume, and if
the hardware permits it, you can rebuild online.
6. Vinum has a whole lot more features, like dynamic reconfiguration,
multiple mirrors, RAID-5 (and RAID-4, because somebody insisted;
don't use it).
Greg
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