Date: Fri, 18 May 2001 10:59:47 +0930 From: Greg Lehey <grog@lemis.com> To: Stephen Cimarelli <stephen@clari.net.au> Cc: Marcus Reid <marcus@blazingdot.com>, Gabriel Ambuehl <gabriel_ambuehl@buz.ch>, Jonathan Fortin <jfortin@akalink.com>, questions@FreeBSD.ORG Subject: Re: Raid (BEST PERFORMANCE) Message-ID: <20010518105947.D55915@wantadilla.lemis.com> In-Reply-To: <XFMail.010518103933.stephen@clari.net.au>; from stephen@clari.net.au on Fri, May 18, 2001 at 10:39:33AM %2B1000 References: <20010517011226.A4473@blazingdot.com> <XFMail.010518103933.stephen@clari.net.au>
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On Friday, 18 May 2001 at 10:39:33 +1000, Stephen Cimarelli wrote:
> On 17-May-01 Marcus Reid wrote:
>> On Thu, May 17, 2001 at 04:50:26PM +0930, Greg Lehey wrote:
>>> On Wednesday, 16 May 2001 at 22:07:48 -0700, Marcus Reid wrote:
>>>> On Tue, May 08, 2001 at 06:22:26PM +0200, Gabriel Ambuehl wrote:
>>>>>
>>>>> Hello Jonathan,
>>>>> Monday, May 07, 2001, 7:08:48 PM, you wrote:
>>>>>> Best Performance Raid is a raid 0+1 setup.
>>>>>> For example, you got 4 20gb harddrives.
>>>>>> You create 2 strips of 2hds eachs, and you mirror them.
>>>>>> It will have redundancy and the speed will be as fast as a normal
>>>>> disk. It's
>>>>>> basically a Raid-1 setup with 2 hard drives per strip instead of one
>>>>> to
>>>>>> counter write performance hits.
>>>>> Some vendors like to call this RAID 10 (hmm. 1+0=10? only if those are
>>>>> strings...).
>>>>
>>>> If I'm not mistaken, there's a difference between 0+1 and 10: one is
>>>> striped and then mirrored, the other is mirrored and then striped. It's
>>>> supposed to have some bearing on performance, 0+1 being the faster one.
>>>
>>> I've heard people make this kind of claim. I can't understand what
>>> the difference is supposed to be. Can you justify it?
>>
>> It's something that I read on the qmail list; people were talking about
>> the best RAID scheme to use for a very high-volume mail server. I don't
>> have anything to offer from personal experience. I'm assembling a new mail
>> machine very soon and have to select which level of RAID to use, so I'd
>> be interested to hear if there's any truth behind it.
>
> Raid levels has seen by Mylex
as?
> Level 0+1 Combines Daid 0 striping and Raid1 mirroring
>
> Level 10 Combines raid0 striping and Raid 1 mirroring spanned across multiple
> drive groups
Hmm. Without defining "drive group", this doesn't say very much.
> level 30 Combines Raid 0 and raid 3 across multiple drive groups
I very much doubt that Mylex implements RAID-3. I suspect they mean
RAID-4. RAID-3 is at sub-sector level.
> Level 50 Combines Raid 0 and raid 5 across multiple drive groups
I wonder how they envisage RAID-5 without striping.
> is there some offical body that decided on what level 10,30,50 are,
> or do companys make up there own
I think many companies make up their own. I've never heard of 30 or
50. I suspect that the distinction between "0+1" and "10" is bogus,
though I'm open to further documentation.
Greg
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