[DRBD-user] How efficient is DRBD during Sync?

Digimer lists at alteeve.ca
Thu Oct 22 07:03:10 CEST 2015

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

On 21/10/15 03:57 PM, Christian Völker wrote:
> Hi all,
> just a simple question for my own curiosity.
> Assume a two node master-slave setup. Disk on the master fails. All
> reads and writes go through the slave (master remains primary).
> Now the disk on the primary is replaced and the full sync is started.
> Now let's say the sync is at 40% and a write occurs which fits into the
> not yet synced 60% of the disk.
> Ist the block now written in parallel to both nodes and marked on the
> primary as "already synced" or does the write affect only the slave and
> during the remaining sync the block is copied back to the primary?
> Just curious....
> Thanks!
> Chrischan

Once connected, all new writes are synchronous, yes. Out of sync blocks
replicate at the resync rate. This is why setting a high resync rate
will slow down applications writing to DRBD because the bandwidth
available for new writes is total capacity minus capacity used by resync.

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