Date: Fri, 6 Mar 2009 14:10:34 +0100 From: Daan Vreeken <Daan@vehosting.nl> To: Christopher Key <cjk32@cam.ac.uk> Cc: freebsd-questions@freebsd.org Subject: Re: SATA Port Multipliers in FreeBSD (6.3) Message-ID: <200903061410.35051.Daan@vehosting.nl> In-Reply-To: <49B11A77.2040801@cam.ac.uk> References: <49AFE0DF.9000003@cam.ac.uk> <200903060103.16752.Daan@vehosting.nl> <49B11A77.2040801@cam.ac.uk>
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On Friday 06 March 2009 13:43:35 Christopher Key wrote: > Daan Vreeken wrote: > > Hi Christopher, > > > > On Thursday 05 March 2009 15:25:35 Christopher Key wrote: > >> Hello, > >> > >> I'm looking to substantially expand the storage on my FreeBSD 6.3 home > >> media server. With regards hardware, the simplest way to attach large > >> numbers of drives seem to be to use SATA port multipliers, but I've be= en > >> unable to find any consensus on their level of support in FreeBSD. I'm > >> currently looking at a RocketRAID 2314 and SiI3726 based port > >> multipliers. Has any had any experience with this combination? > > > > The Sil3726 works very well if you run a recent enough version of > > FreeBSD. We use the device in a custom storage appliance. I don't know > > the RocketRAID 2314 though. You need a SATA 2.0 controller for Port > > Multipliers to work. > > I'm pretty sure the RocketRAID 2314 is a SATA 2.0 controller. I've > references in places to it supporting port multipliers, but have been > unable to to find any further details on quite what this means. To be > honest, I don't fully understand how the ATA system fits together. > HighPoint offer a FreeBSD driver, but I don't know whether this replaces > functionality within FreeBSD, or is an additional requirement. Nor do I > know whether port multiplier support is the responsibility of the ATA > driver, the ATA controller, both or either, nor whether the ATA > controller being a RAID card in JBOD mode affects anything. I was > thinking that for the RR2314 to work with port multipliers whilst it was > doing hardware RAID, it must fully understand how to address drives > behind a port multiplier and might do the same in JBOD mode, simply > presenting the ATA driver with a list of drives. Whether this is valid > reasoning, I've no idea. If the RR2314 controller really does RAID in hardware, then the OS would on= ly=20 see the resulting big 'disks', without needing to know where they came from= =20 and if they are behind Port Multipliers or not. I suspect (but I'm not sure here) that RAID on the RR2314 is implemented by= =20 the driver instead of the hardware. In that case, the OS (or at least the vendor's own driver) needs to know ho= w=20 to handle Port Multipliers. The current state of Port Multipliers in FreeBSD (at least, in the version= =20 we're using on our appliance here) is that it is working very well, but lac= ks=20 some features. Hot-plugging disks for example doesn't work. All disks need = to=20 be present when the system is power up. For us this isn't a problem. > > FreeBSD has (experimental) support for Port Multipliers since the > > following commit : =2E.. > > On Thursday 10 April 2008 15:05:05 S=F8ren Schmidt wrote: > >> sos 2008-04-10 13:05:05 UTC > > Thanks, I've found the relevent revision in SVN, > http://svn.freebsd.org/viewvc/base?view=3Drevision&revision=3D178067 > > I'll read through the diffs to see if I can get a better idea of how > everything works. I you would like to know more about the technical details, I would recommen= d=20 reading the 'Port Multiplier' part of the SATA 2 spec, which can be found=20 here : http://cvs.codeyard.net/svn/SiI24/doc/pm_1_1_Gold.pdf Or you could read this summary on sata-io.org : http://www.sata-io.org/portmultiplier.asp Regards, =2D-=20 Daan Vreeken VEHosting http://VEHosting.nl tel: +31-(0)40-7113050 / +31-(0)6-46210825 KvK nr: 17174380
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