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Re: [Linux-cluster] GFS, iSCSI, multipaths and RAID

Thanks for your response Wendy. Please see a diagram of the system at http://www.ndsg.net.nz/ndsg_cluster.jpg/view (or http://www.ndsg.net.nz/ndsg_cluster.jpg/image_view_fullscreen for the fullscreen view) that (I hope) explains the setup. We are not using FC as we are building the SAN with commodity components (the total cost of the system was less than NZ $9000). The SAN is designed to hold files for staff and students in our department, I'm not sure exactly what applications will use the GFS. We are using iscsi-target software although we may upgrade to using firmware in the future. We have used CLVM on top of software RAID, I agree there are many levels to this system, but I couldn't find the necessary is hardware/software to implement this in a simpler way. I am hoping the list may be helpful here.

What I wanted to do was the following:

Build a SAN from commodity hardware that has no single point of failure and acts like a single file system. The ethernet fabric provide two paths from each server to each storage device (hence two NICs on all the boxes). Each device contains a single logical disk (striped here across two disks for better performance, there is along story behind why we have two disks in each box). These devices (2+) are presented using iSCSI to 2 (or more) servers, but are put together in a RAID-5 configuration so a single failure of a device will not interrupt access to the data.

I used iSCSI as we use ethernet for cost reasons. I used mdadm for multipath as I could not find another way to get the servers to see two iSCSI portals as a single device. I then used mdadm and raided the two iSCSI disks together to get the RAID-5 configuration I wanted. Finally I had to create a logical volume for the GFS system so that servers could properly access the network RAID array. I am more than happy to change this to make it more effective as long as:

1) It doesn't cost very much;
2) The no single point of failure property is maintained;
3) The servers see the SAN as a single entity (that way devices can be added and removed with a minimum of fuss).

Thanks again for any help/advice/suggestions. I am very new to implementing storage networks, so any help is great.

Regards, Mike

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