[DRBD-user] DRBD write speed

Felix Frank ff at mpexnet.de
Mon May 9 18:09:46 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.


Hi,

> I get the feeling that someone needs to read up about caching,
> especially Linux page cache, Linux IO stack,
> and where DRBD is located in there.

never hurts.

> We typically have
>   [ applications ]
>   [ application and library buffers ]
>   [ file systems ]
>   [  page cache  ]
>   [ block layer  ] <=== DRBD lives here
>                   `--- drbd replication via TCP ---> remote "DISK".
>   [    "DISK"    ]

I see.

So my guess that the controller cache is to blame was probably off the
mark, no?

More-than-NIC-capacity throughput could only be facilitated by write
cacheing going on in the page cache or above, as per your diagram.

But I guess I'm still sort of pole-poking the issue.

Thanks for clearing things up!

Felix



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