[DRBD-user] sync with wrong data

Felix Frank ff at mpexnet.de
Mon Jun 4 09:48:36 CEST 2012

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


Hi,

please don't forget to CC the list.

On 06/04/2012 02:58 AM, 陈楠 wrote:
> Thank you! There are volatile write cashes in our I/O system. Does the


As long as you're making use of these caches, you *will* loose data on
power outage or critical hardware failure.
Performance can become unacceptable when you disable them. You can
remedy the situation by protective means such as battery backups or
(preferable imho) flash memory units on your RAID controllers.

> new version has built-in data protection? We have four pairs redundancy

As I said - there is no such thing. DRBD does not know (or care) which
files, buffers or whatever your application is writing to. All it sees
is a stream of blocks. If this stream gets torn, you end up with some
data on your secondary, but it's impossible for DRBD to (e.g.) roll back
to the last sane filesystem state.

> servers, All of them powered off by accident, only one pair servers
> works fine, others all crashed. I think there are something wrong with
> our applications. I want to know how to adapt drbd mechanism for our
> application.

Describe your application then. But DRBD's MO cannot be altered much.

Usually, the type of application that DRBD lends itself well to is one
that can recover from crashes by some means of journal or log. A
prominent example is the InnoDB storage engine in MySQL. A MyISAM
database will not benefit as much from DRBD, because it will likely be
thoroughly corrupted if the primary does crash.

HTH,
Felix



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