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I'm a little bit confused in here..

I want to have 2 node cluster with shared storage. I read all wiki page about HA cluster. Now in my head there's a scheme like: this

So we have two 4U tower servers from superMicro. There's SAS in there... is it possible somehow to connect few servers (not through network) to one SAS storage?? Or we need to sell these two servers and get normal NAS/SAN storage and 2 simple rack servers? Edit: Or just to use these two servers as NAS? and to buy 2 another servers?

any answers are welcome, I'm a little bit a beginner in server hardware so any theory are welcome in here.

Thank you

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yeah switch in graph is kind of in a wrong place nevermind ;D – holms Dec 9 '10 at 14:51
up vote 2 down vote accepted

Do you mean you wanna have concurrent access of a SAS storage server ? With SAS plugs from the two servers ? I'm not quite sure to understand ... But anyway, it would be much simpler to just sell your servers and have a central NAS ( or SAN with iSCSI) with 2-3 gigabit connection, then aggregate all your links together to have higher troughput, you can aggregate the links on your servers too. With this system, you can even plug more and more servers to your NAS/SAN in a far more easier way. And if you go with NAS, when one is full, you can add just a new one, then add a NFS and let's rock'n'roll ;)

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Is it possible to have such a huge connection speed from NAS? at least half of this..? – holms Dec 9 '10 at 15:17
@holms - I've never seen a NAS device with anything higher than a 1Gb interface, which has a real-world maximum speed of around 110MB/sec. However any decent SAN comes in anything up to 10Gbps, of which I've seen transfer speeds of over 1000MB/sec – Mark Henderson Dec 10 '10 at 2:01

Yes. you can get a SAS Switch. They aren't cheap and they aren't well supported for most cluster software, HBAs, or drives. I would recommend getting iSCSI or FC. I've not had good luck with NAS personally, but I know places run it.

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It is indeed possible to connect multiple servers to a single storage device via SAS, but it will depend on the specification of your storage device. If LUN masking is included in the specification then it will likely support multiple devices.

You may also want to reference: Beginner SAS and server questions

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Yes, it is possible to connect 2 servers to a single set of SAS drives. Supermicro makes a drive enclosure that will take 8 2.5" SAS drives and mount in 2 3.5" drive bays. It has two sets of connections, allowing for redundant connections, but this only works on SAS drives (not SATA). It's not clear if a special capability is required from the drives, beyond that it seems clear that SATA does not support this.

That's the theory, I haven't used these devices though I have done some researching of them. So you may need to do some experimentation on this. However, their diagram (on the page referenced below) clearly shows the configuration you are speaking of.

The device is the CSE-M2BE2, and costs just over $200. So much less expensive than any solid ISCSI or SAN solution, and it definitely does not seem to require a SAS switch or the like.

You WILL need to set up and use STONITH to prevent split-brain access of the resources, or use a cluster-aware file-system like OCFS2.

However, using internal drives and DRBD is probably the simplest solution.

If you do get to play around with this, I'd be particularly interested to know how it works.

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We recently discussed something similar. The post offers many good options but we settled on RAID Inc.'s Xandu 230. They will deliver a no-single-point-of-failure redundant 6 Gbps SAS storage shelf (24 bays filled with 2TB 6 Gbps SAS drives).

Please see the accepted answer in this post for technical and pricing details.

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