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I was reading an article on Linux Journal about Memcached and it mentions Netbooting multiple servers off a single root image:

LiveJournal's Web nodes are all diskless, Netbooting off a common yet redundant NFS root image. Not only is this cheaper, but it requires significantly less maintenance.

How does this work with logging? Does each node write to the same place? What about configuring static ip addresses? If machine A writes to the disk, does machine B pick it up? When he says "web node" does he mean just the web server? I'm assuming this means the web application as well (PHP/Perl), correct?

Is this even a good idea (with mostly using RAM)?

Can this same thing be done with iSCISI?

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Logging would typically be done by setting up the syslog to write to a central location over the network. syslog can do this with minimal changes. The server syslog has to be configured to accept TCP connections, the clients then are told to write to that server.

For things like Apache, you'd probably have it write to different directories based on the name, or you could pump it to syslog or something...

Is it a good idea? Sure, works great!

The same thing is not as easy to do with iSCSI, you'd have to have the root partition be on a clustered file-system such as OCFS or GFS, iSCSI is not a file-system, it's a networked block device.

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The datacenter I use offers iSCSI on their servers. I'm wondering if it's possible to mount a iSCISI partition on two servers at the same time. I ask because we're thinking about using iSCISI vs physical media. It would be cool if I could setup a single "web node" partition and mount that disk to several servers. – Luke Sep 28 '11 at 3:43
As I said, no you can't really do the same with iSCSI. Unless you mount the file-systems read-only. – Sean Reifschneider Sep 28 '11 at 3:46
Ah, ok! So with Netboot it can be read/write? Would there be any advantage in mounting iSCSI as read-only verses Netboot over NFS? – Luke Sep 28 '11 at 3:50
Well, you obviously have to adjust things so that servers aren't conflicting with writing the data to the same files when you do an NFS discless setup. iSCSI read-only setup is likely to be much more difficult, because you will have to make sure that NO writes are being done on that file-system, where with NFS you just have to make sure that it isn't conflicting, and they CAN write to their root. Most distro installs aren't set up to have a truly read-only root filesystem, so that requires more work. – Sean Reifschneider Sep 28 '11 at 21:46
Cool, good to know! – Luke Sep 28 '11 at 22:46

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