DragonFly users List (threaded) for 2009-01
From: =?ISO-8859-1?Q?Bj=F8rn_Vermo?= <email@example.com>
Subject: Re: RAID 1 or Hammer
Date: Wed, 14 Jan 2009 14:05:46 +0100
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References: <496b8121$0$881$415eb37d@crater_reader.dragonflybsd.org> <496b961e$0$882$415eb37d@crater_reader.dragonflybsd.org> <882FE201-9FFB-40B7-A945-DD21337DD661@freemail.gr> <496BC215.firstname.lastname@example.org> <email@example.com> <200901130315.n0D3FlP9038935@apollo.backplane.com> <E663E77A-8DA0-4294-88E5-961385920B4D@opera.com> <496DA32B.firstname.lastname@example.org> <EC89B64F-B8C1-498A-8489-4258865E1CB4@opera.com> <6D9E2264-1DAD-4B23-A03F-0636D24C363E@yberwaffe.c
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On 14. jan.. 2009, at 12.17, Jasse Jansson wrote:
> First of all, thanks Simon for the links, It sure was interesting =20
> On Jan 14, 2009, at 11:45 AM, Bj=F8rn Vermo wrote:
>> I have toyed with the idea that one drive in a mirrored pair ought =20=
>> to have the addresses inverted, so sector 1 on one drive is mapped =20=
>> to sector MAX -1 on the other.
> I read it like the locality (radius) of the errors occur on the same =20=
> so I don't see the benefit from your "reversed mirror strategy".
He clearly stated that some drives models had error spikes at certain =20=
This should not really surprise anybody who is familiar with the way =20
modern drives work internally. The cylinder where you change to a =20
different data density is a border case, and any border cases open =20
extra bug opportunities.
> You will also get some interesting performance problems to tackle, =20
> one disc works on the inner tracks and the other one is on the outer =20=
A smart controller could make that into an opportunity. It is hardly =20
any more difficult than staggered stripes, which is widely implemented.
In most mirroring controllers I have seen the system will get the read =20=
data from the first drive that has them ready. Two "opposite" drives =20
should be able to offer a better average read performance.
Opera Software ASA