Nicolas Ross wrote:
Thanks
If you want the FS mounted on all nodes at the same time then all
those nodes must be a part of the cluster, and they have to be quorate
(majority of nodes have to be up). You don't need a quorum block
device, but it can be useful when you have only 2 nodes.
At term, I will have 7 to 10 nodes, but 2 at first for initial setup and
testing. Ok, so if I have a 3 nodes cluster for exemple, I need at least
2 nodes for the cluster, and thus the gfs, to be up ? I cannot have a
running gfs with only one node ?
In a 2-node cluster, you can have running GFS with just one node up. But
in that case it is advisble to have a quorum block device on the SAN.
With a 3 node cluster, you cannot have quorum with just 1 node, and thus
you cannot have GFS running. It will block until quorum is re-established.
If you are only ever going to have the SAN volume mounted on one
device at a time, don't bother with GFS and make the SAN block device
a fail-over resource so that only one node can mount it at a time, and
put a normal non-shared FS on it. You will get better performance.
I do need a shared file-system, I am aware of the added latency, we
currently have some latency on our xSan setup. But we do also need on
some services an additional block-device that is accessed only by one
node and is indeed failed-over another node when a node fail.
So handle the file system failover for the ones where only one node
accesses them at a time and have a shared file system for the areas
where multiple nodes need concurrent access.
The number of journals needs to be equal to or greater than the number
of nodes you have in a cluster. e.g. if you have 5 nodes in a cluster,
you need at least 5 journals. If you think you might upgrade your
cluster to 10 nodes at some point in the future, then create 10
journals, as this needs to be done at FS creation time.
That I got. It's the size that I don't know how to figure out. Will 32
megs will be enough ? 64 ? 128 ?
That depends largely on how big your operations are. I cannot remember
what the defaults are, but they are reasonable. In general, big journals
can help if you do big I/O operations. In practice, block group sizes
can be more important for performance (bigger can help on very large
file systems or big files).
Gordan
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