[DRBD-user] replication link stability

Arnold Krille arnold at arnoldarts.de
Thu Feb 16 16:30:36 CET 2012


On Thursday 16 February 2012 15:18:05 Piotr Kandziora wrote:
> Hi,
> 
> I have two servers with dedicated replication link (WiFI - 48Mbit/s). My
> clients are connecting via other network link (100Mbit/s) to SAMBA service.

Rofl!

Sorry, spend the 10€ per server to get them dedicated 100MBit cards. It will 
do you a great favour.
But unless you spend 20€ per server for Gigabit cards, it will still be slow 
as hell...

The wifi is not only bad for your throughput: 48MBit/s is low compared to 
120MBytes/s  for direct disk access. Its actually half of that because wifi is 
half-duplex by design.
100MBit will be a bit better as you then have ~12MByte/s per direction.
Only Gigabit will really keep up with the throughput of the disk.

Additionally wifi has the ethernet-latency plus the wireless-latency plus the 
latency of half-duplex and collision-detection.

It is a) no wonder your users will be complaining about the poor performance 
(mine are still complaining while I have a dedicated GB-link) and b) its no 
wonder drbd complains and stops the sync...

Have fun,

Arnold
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