[DRBD-user] Is `sync` option of ext3 mount SHOULD used in drbd HA clusters?

Pan'ko Alexandr A.Panko at infocom.dn.ua
Tue Sep 16 10:09:38 CEST 2008

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

В Пнд, 15/09/2008 в 12:09 -0400, Greg Freemyer пишет:

> Alexandr,
> I believe the issue is that you need to consider the robustness of
> your programs standalone prior to considering drbd's behavior.  ie.
> What happens to the data your application is processing if you pull
> the power cord with no warning?  Is the app robust enough to address
> this?
> For instance, a well written database uses ACID.
> (http://en.wikipedia.org/wiki/ACID)
> That ensures that when a system running a database stops unexpectedly
> and then is restarted, the database will be in a well known state.
> Simple utilities like dd and cp do not make any effort to ensure the
> robustness of their disk activities in the presence of system
> failures.  Therefore drbd has no ability to function the way you
> desire.
> For tools that properly use commands like fsync to ensure robustness
> in the presence of system failure drbd should be a good solution.
> Your idea of using the sync mount option or calling fsync after every
> byte is a sledgehammer approach but even it will not work if the
> applications you want to use are not designed to work in the presence
> of system failures.
> ie. The app has 2 things it needs to update "atomically".  They
> obviously happen sequentially in the real world, so what happens if
> the system fails between the first and second activity getting to
> disk.  A well written application will have support code to address
> this.  Simply calling fsync after every write does NOT do so.
> Greg

Thank you, Greg!
It's very clean and understandable explanation.
I even think it is worth to add to FAQ or HOWTO.

Tank you again!

Regards, Alexandr A. Panko

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