Date: Tue, 22 Nov 2005 10:03:43 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Wojciech Puchar <wojtek@tensor.3miasto.net> Cc: freebsd-questions@freebsd.org, John Oxley <john@yoafrica.com> Subject: Re: iSCSI support Message-ID: <20051122160343.GB6893@dan.emsphone.com> In-Reply-To: <20051122121855.J89225@chylonia.3miasto.net> References: <43824EF0.8090807@endries.org> <20051122002352.G75644@chylonia.3miasto.net> <20051122062506.GD13838@yoafrica.com> <20051122121855.J89225@chylonia.3miasto.net>
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In the last episode (Nov 22), Wojciech Puchar said: > >>from people. > > > >ICBW but to me it seems that iSCSI is like a distributed NFS backend. You > >can > >store the data on multiple devices, in multiple forms (as long as they > >all talk iSCSI). You can also have two storage sites (geographically > >separate) connected by fibre and use those for storage. > same as NFS. while with iSCSI you have exported whole devices that can't > be really shared with ease. and 100 times more expensive of course that > just a cheap PC with cheap IDE drives.. Whole devices accessed directly can be a lot faster than NFS, since the client doesn't have to constantly ask the NFS server whether the file it's currently accessing has changed. And when a cheap IDE in one of the 100 servers in your server room goes out, you have to find the server, figure out which drives it has in it and which RAID controller it has, go to your spares cabinet and get the right spare, swap the drive, load your raid management software, and rebuild. Unless you have a hotspare in each computer, but that's quite a lot of wasted disks. With a iSCSI/FC SAN setup, you probably have a couple hotspares configured in your array already and it's rebuilt automatically. If a server needs a few more TB or storage, simply create a new LUN and make it visible to the server. If you want to set up failover (or are running an OS that has clustered filesystems), make one LUN visible to multiple machines. There's also nothing that says the disks behind the iSCSI array can't be cheap IDE drives. -- Dan Nelson dnelson@allantgroup.com
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