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On Thursday 25 May 2006 14:13, "Bruno Lustosa" <bruno.lists@×××××.com> |
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wrote about '[gentoo-user] Linux Cluster': |
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> - Distributed filesystem, so that all machines can share the same |
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> filesystem. Something like RAID-over-ethernet. |
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You probably want RH's GFS (there are probably other cluster-aware |
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filesystems available for linux that I'm not aware of) and some sort of |
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external storage that allows you to hook two machines to it. You might |
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also look into multipathing, that would help in case of a cable failure. |
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For maximum availability, you want your enclosure to have two scsi disk |
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controllers, each with two separate scsi ports (these ports are on |
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different chains). You'll hook each of the two computers into cluster to |
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one port on each controller and then use multipathing to tell linux both |
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scsi paths are the same device. You'll have a second external storage |
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connected the same way and software use software mirroring. Then, |
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partition the mirror set (you could also partition at the external |
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storage, but then you have to update the partitions on each storage) and |
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lay GFS down. |
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At this point, you don't lose connectivity to your storage if a cable, an |
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hba, an enclosure, a controller, or a computer goes down. Of course, the |
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controllers will handle RAID 5 or RAID 6 so you won't lose even a single |
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path in case of HD failure. GFS should allow concurrent access -- |
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possibly even with multiple r/w mounts. ext2/3, jfs, xfs, reiserfs, and |
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even reiser4 are not cluster aware so they will only work properly in the |
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configuration with multiple r/o mounts *OR* a single r/w mount. |
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> - Load balancing. Tasks should migrate between nodes. |
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HP's ServiceGuard for linux is the only software I know that will do this |
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(for this *sure* there are other commerical solutions), and there is still |
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some small amount of downtime when a task migrates, so they aren't |
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automatically generated. |
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Also, some software (IIRC, WebLogic) is able to exist in a clustered |
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environment with some method to sync state across individual nodes |
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(possibly using the clustered FS) so that instead of |
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jobs/packages/daemons/tasks migrating it just runs on all nodes all the |
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time. |
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The second option (a cluster-aware program) is usually preferable, because |
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the program itself is better at determining what state needs to be shared, |
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so you get less intra-node communication and less downtime in case a node |
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fails. *However*, an external failover/load-balancer may either be your |
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only solution (if you are already attached to a certain, non-cluster-aware |
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program) or provide better behavior in the case the program is buggy |
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(especially if it's failure mode corrupts and/or brings down other nodes). |
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> - Redundancy, so that the death of a machine doesn't take the cluster |
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> or any processes down. |
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I believe there's a userland implementation of the CARP protocol that may |
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work for linux. It allows 2 (or more) machines on the same network to |
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share an IP and failover and/or load-balance handling packets directed to |
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that IP. |
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> So, anyone doing linux clusters? |
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Not personally, but I was looking into them some during my last job. |
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(Trying to get a customer to switch to linux.) |
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-- |
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"If there's one thing we've established over the years, |
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it's that the vast majority of our users don't have the slightest |
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clue what's best for them in terms of package stability." |
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-- Gentoo Developer Ciaran McCreesh |
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