On Sat, Oct 10, 2009 at 09:05:32PM +0100, Corey Kovacs wrote: > One thing to keep in mind is the fact that iscsi is a tcp based protocol. > So even though your machine might be doing nothing but acting as an iscsi > target, it's going to take the brunt of the load in handling the tcp > stack. If you can get a network card that handles iscsi on the card > itself, that will help loads. Otherwise your cpu might dig a hole for > itself to crawl into. > I don't think iSCSI HBA drivers to use in the _target_ are publicly available. iSCSI HBA's in the initiator (client) are supported of course. Then again most NICs nowadays offload TCP/IP, and most can also offload iSCSI.. HBAs are getting legacy stuff. > Of course if your just messing about, or only using the iscsi targets > locally, then your probably ok. > > Benefits of a dedicated device are management capabilities, throughput, > flexible location, etc. Fibre channel is 8Gb standard now and SAN's are > starting to use it instead of 4Gb, but the entry point in terms of cost is > high. A fully loaded EVA8100 can cost 250k, the FC infrastructure can go > to 60-80k easily. iscsi really needs to have a seperate back end storage > network to be useful and it should be 10Gb. I hear people say it's useful > on slower hardware but everyone has an opinion. I guess if your just using > it for system volumes and low IO then 1G might be fine. > 1G iSCSI works very well for many workloads, depending mostly on your storage/target setup. 1G link can handle a lot of random IOs.. you're most probably limited by the amount of disk spindles anyway. FC is getting legacy aswell.. IMHO :) -- Pasi > Anyway hope this help and if it doesnt' at least it might give you more to > think about. > > Best of luck > > Corey > > On Sat, Oct 10, 2009 at 8:41 PM, Madison Kelly <[1]linux@xxxxxxxxxxx> > wrote: > > Andrew A. Neuschwander wrote: > > Madison Kelly wrote: > > Hi all, > > Until now, I've been building 2-node clusters using DRBD+LVM for > the shared storage. I've been teaching myself clustering, so I don't > have a world of capital to sink into hardware at the moment. I would > like to start getting some experience with 3+ nodes using a central > SAN disk. > > So I've been pricing out the minimal hardware for a four-node > cluster and have something to start with. My current hiccup though > is the SAN side. I've searched around, but have not been able to get > a clear answer. > > Is it possible to build a host machine (CentOS/Debian) to have a > simple MD device and make it available to the cluster nodes as an > iSCSI/SAN device? Being a learning exercise, I am not too worried > about speed or redundancy (beyond testing failure types and > recovery). > > Thanks for any insight, advice, pointers! > > Madi > > If you want to use a Linux host as a iscsi 'server' (a target in iscsi > terminiology), you can use IET, the iSCSI Enterprise Target: > [2]http://iscsitarget.sourceforge.net/. I've used it and it works > well, but it is a little CPU hungry. Obviously, you don't get the > benefits of a hardware SAN, but you don't get the cost either. > > -Andrew > > Thanks, Andrew! I'll go look at that now. > > I was planning on building my SAN server on an core2duo-based system > with 2GB of RAM. I figured that the server will do nothing but > host/handle the SAN/iSCSI stuff, so the CPU consumption should be fine. > Is there a way to quantify the "CPU/Memory hungry"-ness of running a SAN > box? Ie: what does a given read/write/etc call "cost"? > > As an aside, beyond hot-swap/bandwidth/quality, what generally is the > "advantage" of dedicated SAN/iSCSI hardware vs. white box roll-your-own? > > Thanks again! > > Madi > -- > Linux-cluster mailing list > [3]Linux-cluster@xxxxxxxxxx > [4]https://www.redhat.com/mailman/listinfo/linux-cluster > > References > > Visible links > 1. mailto:linux@xxxxxxxxxxx > 2. http://iscsitarget.sourceforge.net/ > 3. mailto:Linux-cluster@xxxxxxxxxx > 4. https://www.redhat.com/mailman/listinfo/linux-cluster > -- > Linux-cluster mailing list > Linux-cluster@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/linux-cluster -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
