[DRBD-user] Question on local block error behavior

Florian Haas florian at hastexo.com
Fri Oct 14 09:02:47 CEST 2011

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


On 2011-10-13 20:00, Jojy Varghese wrote:
> Hi
>    We are testing drbd for our storage cluster and had a question
> about the behavior we are seeing. we have layered drbd on top of a
> device mapper layer. When we simulate a block error using the dm
> layer, we see that the requests for those particular blocks is
> forwarded to the peer node. We are using 8.3x version of drbd. The
> documentation says that the default behavior is to takeout the
> defective node even if there is 1 block error.

Er, no. It never was, and the documentation (at least the User's Guide)
never said so.

- Prior to 8.4, the default behavior was to simply not do anything about
the I/O error and pass it right up to the calling layer, where the
latter was expected to handle it.

http://www.drbd.org/users-guide-legacy/s-configure-io-error-behavior.html

- Since 8.4, the default behavior is to transparently read from or write
to the affected block on the peer node, "detaching" from the local
(faulty) device and masking the I/O error.

http://www.drbd.org/users-guide/s-configure-io-error-behavior.html

Removal from the cluster in case of an I/O error (by way of a deliberate
kernel panic) was an option in 0.7, and can still be configured via a
local-io-error handler. If it was ever the default, then that would have
been prior to 0.7 -- i.e. long before I started working with DRBD, so I
wouldn't know.

Hope this helps.

Cheers,
Florian

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