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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