Mirrored Filesystems

Hi,

I'm looking for a way to mirror a filesystem over a network so that two
servers can be kept up to date with each other in realtime. I.e if a user
ftps a file to server A, server B will automatically realise this and
update its own filesystem accordingly. The goal of this is a set of load
balancing web servers that aren't dependent on a centralised file server,
so that if we need to upgrade the disk space we can just pull them out one
at a time to add new disks.
I've looked at AFS, but i'm not entirely sure if thats what i'm looking
for... Software raid like that found at http://www.drbd.org/ could also be
an option, but i'm not sure how reliable such a solution would be.

If anyone could offer advice as to the best way to go about this, or offer
any better suggestions, I woudl be very grateful.

Daniel Andersen

Hi Daniel,

> I'm looking for a way to mirror a filesystem over a network so that two
> servers can be kept up to date with each other in realtime. I.e if a user
> ftps a file to server A, server B will automatically realise this and
> update its own filesystem accordingly. The goal of this is a set of load
> balancing web servers that aren't dependent on a centralised file server,
> so that if we need to upgrade the disk space we can just pull them out one
> at a time to add new disks.
> I've looked at AFS, but i'm not entirely sure if thats what i'm looking
> for... Software raid like that found at http://www.drbd.org/ could also be
> an option, but i'm not sure how reliable such a solution would be.
>
> If anyone could offer advice as to the best way to go about this, or offer
> any better suggestions, I woudl be very grateful.
>

I think that rsync may do the job for you, have a look at the rsynce website
http://www.rsync.org/**this*may*also*assist
http://sunsite.dk/info/guides/rsync/...mirroring.html
*or*google*for*rsync.

I haven't used rsync myself, but have been looking at it for local lan
backups.

HTH

-----
John

Pls remove xxnospam for email replies

On Friday 21 November 2003 11:58, john wrote:

> Hi Daniel,
>
>
> I haven't used rsync myself, but have been looking at it for local lan
> backups.
>

Is this realtime though? I was under the impression rsync had to be run each
time you wanted an update, which is not really what I'm after.
Inconsistencies between the load-shared servers would only cause problems.

Daniel

Daniel Andersen wrote:

> On Friday 21 November 2003 11:58, john wrote:
>
>> Hi Daniel,
>>
>>
>> I haven't used rsync myself, but have been looking at it for local lan
>> backups.
>>
>
> Is this realtime though? I was under the impression rsync had to be run
> each time you wanted an update, which is not really what I'm after.
> Inconsistencies between the load-shared servers would only cause problems.
>
> Daniel

I'm not sure about realtime, you may need to check out the website for the
answer to that, but even so what about a cron job every 5 mins or so?
Rsync only changes files it needs to.
--
-----
John

Pls remove xxnospam for email replies

On Friday 21 November 2003 15:03, john wrote:

> Daniel Andersen wrote:
>
>> On Friday 21 November 2003 11:58, john wrote:
>>
>>> Hi Daniel,
>>>
>>>
>>> I haven't used rsync myself, but have been looking at it for local lan
>>> backups.
>>>
>>
>> Is this realtime though? I was under the impression rsync had to be run
>> each time you wanted an update, which is not really what I'm after.
>> Inconsistencies between the load-shared servers would only cause
>> problems.
>>
>> Daniel
>
> I'm not sure about realtime, you may need to check out the website for the
> answer to that, but even so what about a cron job every 5 mins or so?
> Rsync only changes files it needs to.

No even five minutes isn't realtime enough. The real problem is, say, if a
customer updates a page on their website on server A, then refreshes the
page in their browser to see how it looks. If they load balancing sumbits
their request to server B, which might not have updated yet, then the
customer would get very confused, whcih is a bad thing
Thus the need for a realtime system rather than a not-quite-realtime system.

Daniel

Daniel Andersen schreef:
> Hi,
>
> I'm looking for a way to mirror a filesystem over a network so that two
> servers can be kept up to date with each other in realtime.
[snip]

You could set up coda on both systems
http://www.coda.cs.cmu.edu/


> Software raid like that found at http://www.drbd.org/ could also be
> an option, but i'm not sure how reliable such a solution would be.

As far as I know sofware raid is reliable, only it is used to mirror
data localy, not on another pc as you wish to do.


Hope this helps,
Sanne

On Saturday 22 November 2003 23:20, Sanne ;0) wrote:


> You could set up coda on both systems
> http://www.coda.cs.cmu.edu/
>

Yeah i looked into coda but I'm not sure how reliable it is. Does anyone out
there use Coda in a production environment and can offer some comments on
how well it works? The fact that its up to version 6 or so suggests a
certain amount of maturity, but i'm a bit dubious about trusting my servers
to an unknown quantity At anyrate i'll give it a try and see how it goes
after some testing, but once again any advice on how well it runs or setup
hints would be very helpful.

Daniel

Daniel Andersen schreef:
> I'm looking for a way to mirror a filesystem over a network so that two
> servers can be kept up to date with each other in realtime.

"Sanne ;0)" <(E-Mail Removed)> wrote:
> As far as I know sofware raid is reliable, only it is used to mirror
> data localy, not on another pc as you wish to do.

See groups.google.com/groups?as_umsgid=fmek61-sci.ln1%40news.roaima.co.uk
for an answer regarding Network Software RAID.

Chris