Date: Fri, 23 Apr 2010 16:03:58 +0200 From: Bernd Walter <ticso@cicely7.cicely.de> To: John Baldwin <jhb@freebsd.org> Cc: Alexander Motin <mav@freebsd.org>, freebsd-current@freebsd.org, freebsd-geom@freebsd.org Subject: Re: Switchover to CAM ATA? Message-ID: <20100423140358.GC1575@cicely7.cicely.de> In-Reply-To: <201004230950.33999.jhb@freebsd.org> References: <4BD06BD9.6030401@FreeBSD.org> <201004230950.33999.jhb@freebsd.org>
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On Fri, Apr 23, 2010 at 09:50:33AM -0400, John Baldwin wrote: > On Thursday 22 April 2010 11:31:37 am Alexander Motin wrote: > > If ataraid(4) should be reimplemented in GEOM, then how exactly? One > > more separate RAID infrastructure in GEOM (third?) looks excessive. > > Reuse gmirror, gstripe,... code would be nice, but will make them more > > complicated and could be not easy for RAID0+1 (due to common metadata) > > and RAID5 (due to lack of module in a base system). > > Scott's view (which sounds good to me) is that GEOM should include a library > of routines for working with common transforms such as RAID1, striping, etc. > Each ATA RAID vendor format would then consist of a small GEOM module that > used the library routines to manage all the I/O and the bulk of the module > would be managing a specific metadata format. I remember that SCSI standard has support for xor read-modify-write operations in addition to normal read/write to reduce R5 latency and bandwith. I'm not sure if any devices actually support it, but I think this may be worthwhile for networked devices. -- B.Walter <bernd@bwct.de> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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