Hi list,
I have a question about the feasibility of a dual primary setup over two
VDSL WAN links. I already searched the list and I found similar
question, but without having a definitive conclusion.
My goal is to have a shared fileserver over two distant offices, using
DRBD to create the illusion of a single block devices. I plan to use
GFS2 (or OCFS) filesystem, exporting it to users (on both side) via
Samaba shares.
Please note that:
1) both server are CentOS 6.x x86_64 machines, with DRBD packages
provided by ElRepo (DRBD 8.4.x)
2) the main and remote offices are connected with relatively fast (~100
Mb/s) but high latency (+30 ms RTT) VDSL links
3) write speed should be as high as possible
My current understanding (correct me if wrong) is that:
1) to not impair write speed, I should use protocol A
2) GFS2 (or any cluster filesystem) is quite sensitive to latency, so
some operation (eg: metadata mangling, locking, reading an alredy
remote-opened files) will be slowed down anyway
3) all will work (more or less) fine unless the WAN/VPN goes down.
It is the "WAN failed" scenario that puzzle me. Let me do some questions:
1) at the block/device level, will both hosts (being both primary nodes)
continue to accept writes? If so, will they end in a "split brain"
scenario, right?
2) will the higher level filesystem (eg: GFS2) will block until the
remote connection is re-established?
3) what will happens at connection recover?
I understand that I can try myself (and I am going to do it, indeed),
however I can only test on a fast LAN, not on a (relatively) slow WAN link.
Thank you all.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.da...@assyoma.it - i...@assyoma.it
GPG public key ID: FF5F32A8
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