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Suggestions for simple, RELIABLE NAS?
We currently have a NAS solution that, while it more-than meets our
need in storage capacity and performance, isn't as reliable as we'd like: 2 hosts attached to the same SCSI bus, using a commercial clustering software to failover NFS and IP between 2 hosts. Obviously, the SCSI chain is a single-point-of-failure, and it's bitten us several times. I'm looking for alternatives. We don't need much scalability: 1 40GB filesystem and 1 60GB filesystem is more than we'll need in the foreseeable future. We don't need much performance: both filesystems are used mostly for applications reading config files during startup (and that doesn't happen often; even when it does, disk IO is still very low); So we just need reliability. And I'd like to eliminate the "one SCSI bus" as a SPOF. So I'd really appreciate suggestions on alternate configurations. The only thing I can think of that might resolve our SCSI issue would be to setup some kind of data replication (VVR or an equivalent, perhaps)?; the destination filesystem would handle NFS once the IP used for NFS was failed over (but then what about nfs file locks, and other stuff?). Help/ideas greatly appreciated. |
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"Beeblebrox" wrote in message om... (Beeblebrox) wrote in message . com... We currently have a NAS solution that, while it more-than meets our need in storage capacity and performance, isn't as reliable as we'd like: 2 hosts attached to the same SCSI bus, using a commercial clustering software to failover NFS and IP between 2 hosts. Obviously, the SCSI chain is a single-point-of-failure, and it's bitten us several times. I'm looking for alternatives. We don't need much scalability: 1 40GB filesystem and 1 60GB filesystem is more than we'll need in the foreseeable future. We don't need much performance: both filesystems are used mostly for applications reading config files during startup (and that doesn't happen often; even when it does, disk IO is still very low); So we just need reliability. And I'd like to eliminate the "one SCSI bus" as a SPOF. So I'd really appreciate suggestions on alternate configurations. The only thing I can think of that might resolve our SCSI issue would be to setup some kind of data replication (VVR or an equivalent, perhaps)?; the destination filesystem would handle NFS once the IP used for NFS was failed over (but then what about nfs file locks, and other stuff?). Help/ideas greatly appreciated. Ah, so I've STUMPED this usenet group! Cool. I'm blazing new territory! That's cool. Blazing new territory is why I make the big bucks! While I've got a pretty good idea of what would meet your requirements, I don't happen to know whether anyone has built it. What I'd do is use a pair of servers with directly-attached storage (i.e., inexpensive hardware, though ECC memory would be good), one being primary and one a secondary to which all updates were mirrored in a quasi-transactional manner (i.e., a software solution avoiding both the expense and the complexity of concurrently-shared - or even failover-shared - storage). IP failover would work as it does in your current system. Additional bells and whistles which you wouldn't need include logical update-mirroring at the file rather than the storage-block level (the secondary manages its own metadata independently in such a case, which since it isn't doing anything else useful is reasonable) and/or concurrent use of the secondary to split the workload. The latter gets a bit more complex: if the secondary is simply a standby mirror that takes over on primary failure, you can mirror at the storage-block level via driver-level software (though this requires that metadata updates associated with a data update get sent over the interconnect as block changes rather than being implicit in the single data update message) and, if you're using a log-protected file system like ext3fs, limit most added complexity to that special disk-level driver - Linux actually has such mirroring drivers, but whether there's a surrounding package that would give you everything you're looking for I don't know (and one of the important things is some guarantee that once the system fails over to the secondary it won't fail *back* to the primary without appropriate clean-up of the primary's disk content, which can be at least - and for at least simple implementations at most - one disk-write out of synch with the secondary on any fail-over). As for reestablishing NFS lock context, I'm pretty sure that Sun had mechanisms to do that with its early cluster software, and my impression was that they were incorporated into NFS rather than being proprietary - but I don't know in any detail. Of course, if you want *really* high levels of reliability you'll need truly fault-tolerant hardware (from Tandem or Stratus) on your servers (lacking that, operating and file system software that's suitably paranoid about issuing internal sanity-checks is good for ensuring 'fail-fast' operation that stops the server before it can contaminate its partner), storage software that continually checks the readability of all data so that if a disk fails you aren't likely to find that one of the sectors on the mirror copy has quietly become unreadable, and a file system that aggressively validates stored content against separate checksums (to catch otherwise undetected bus errors, for example, before they can contaminate the mirror copies). - bill |
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