On Sun, Sep 20, 2009 at 11:33 AM, Jussi Peltola <pe...@pelzi.net> wrote: > On Sun, Sep 20, 2009 at 10:58:56AM +0200, Benoit Chesneau wrote: >> Hi all, >> >> I have to setup a full redundant installation for a web services in >> view of having failover from one machine to the other. So data need >> to be replicated fin quasi realtime. There is solution like drbd on >> linux that works like a raid1 over tcp, but I wonder if there is any >> solution that would allow me to do it on openbsd ? also is there any >> distributed fs that could work over openbsd ? > > If your reliability requirements are higher than "in the unlikely event > hardware breaks, someone walks up to the rack and moves the disks to > the cold spare machine", you have a heck of a lot more cases to think > about first. DRBD is a RAID and the same rules of RAID and backups > apply. What if some of your data gets corrupted? How do you recover and > how long will *that* take? How will you handle upgrades - will you only > mirror data or larger parts of the OS? How long would it even take to > fsck the DRBD volume after the primary machine crashes, and how long is > that compared to swapping the disks? > > One way to think about, for a typical DB based web service, is to rsync > your static files in cron and use your database's built in replication > and other redundancy features you need. Real databases are designed to > have ACID transactions, to get that with a filesystem you need more than > DRBD. This way you also get two hot servers for your service instead of > a slightly improved cold spare, which DRBD is. > > Don't get me wrong, though, DRBD does have some good uses that come to > mind, like mirroring a mail server filesystem so you can take snapshots > and run backups off them on another machine to avoid load on the real > server. But it is not a magic 100% uptime dust, since it only really > guards against hardware failure and not against user or software errors. >
I understand the point. My problem was more that couchdb only replicate per db and don't handle global replication of a couchdb node. But I could work with it. Thanks for the enlightenment anyway. - benont
