RE: HA with CentOS

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> -----Original Message-----
> From: centos-bounces@xxxxxxxxxx 
> [mailto:centos-bounces@xxxxxxxxxx] On Behalf Of Ruslan Sivak
> Sent: Monday, May 14, 2007 10:56 AM
> To: CentOS mailing list
> Subject: Re:  HA with CentOS
> 
> Steve Huff wrote:
> >
> > On May 14, 2007, at 10:25 AM, Ruslan Sivak wrote:
> >
> >> Steve Huff wrote:
> >>
> >> If you set up a third box to be the shared storage, 
> doesn't that now 
> >> become the single point of failure?
> >
> > Short answer: maybe. :)
> >
> > Longer answer: If you set up your shared storage according to 
> > upstream's guidelines, as described in the documentation 
> > 
> (http://mirror.centos.org/centos/4/docs/html/rh-cs-en-4/ch-har
> dware.html#TB-HARDWARE-NOSPOF), 
> > then you provide at least two channels of communication 
> between each 
> > component in the cluster.  In addition, you choose a platform for 
> > shared storage that provides some redundancy of its own, 
> whether it's 
> > multi-controller HW RAID, or multiple storage nodes on a 
> SAN, or what 
> > have you.
> >
> > CS/GFS operates under the assumption that your shared storage is 
> > fault-tolerant; its job is to make your services 
> fault-tolerant.  Is 
> > the recommended "no single point of failure" configuration proof 
> > against your data center burning down, or against a madman with an 
> > axe?  Unlikely.  Will it allow you to host services in a 
> way that is 
> > considerably more robust and flexible than hosting them on a single 
> > box?  Yes.
> >
> > -Steve
> >
> 
> I am currently running a redundant environment on windows by having 2 
> boxes with apache and having the data (images) be synced over 
> automatically between servers using FRS (File Replication Service).   
> This works well most of the time, except for when it breaks, at which 
> point I need to resync the two servers, which usually takes days. 
> 
> I would like to set up something similar using linux.  I 
> don't have the 
> budget for a SAN/NAS, and even having a third server as storage would 
> probably not be worth it, although we can possibly go with this.  The 
> problem, is that it would be a single point of failure. 
> 
> Is there some service/filesystem in Linux that allows for the 
> automatic 
> replication of files to make a fault tolerant environment 
> possible with 
> only 2 servers?  Basically whenever there is an update of a file on a 
> certain file system (certain folder), the file gets synced over to 
> another system. 
> 
> Russ

You can check out DRBD, it does block-level replication of data.

-Ross

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