[DRBD-user] Bandwidth limit?

Lars Ellenberg lars.ellenberg at linbit.com
Tue Dec 9 10:39:23 CET 2008

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


On Mon, Dec 08, 2008 at 02:17:50PM -0800, Ben Chobot wrote:
> My understanding is that the minimum bandwidth DRBD needs depends 
> entirely on how fast you're writing data and how much latency you're will 
> to put up with/how big your buffers are. If you're okay with absurdly 
> long writes and don't write very much/often, you could run it over a 
> modem.
>
> Or so goes my understanding. :)

put an other way:
if you write a 1 MByte file to a DRBD, and fsync it,
and your replication bandwidth is 200 kByte/sec,
it will take five seconds.
if that was 200 kBit/sec,
well, it will take 40 seconds.

and that does not take latency into account at all.

you should definetely mount noatime.

and probably rethink your needs.

> On Mon, 8 Dec 2008, Lorenzo Milesi wrote:
>
>> Hi all...
>>
>> I already wrote before on the list about the solution I have at a
>> customer running DRBD8+OCFS2 on two remote sites connected via VPN.
>> The situation is resumed as:
>> SITE A: Dual Core 2GHz Pentium, 1Gb ram, 1 SATA hdd for /, 3 SATA hdd in
>> software raid5, DRBD on /dev/md0.
>> SITE B: Quad Core 2.4HGz Pentium, 2Gb ram, 3 SATA HDD in software raid5,
>> DRBD on /dev/md1.
>>
>> The two sites are connected using two ADSL, with TWO bonded VPN.
>>
>> Both machines run Debian Etch fully updated, kernel 2.6.26-bpo.1-686 SMP
>> with deadline scheduler, DRBD 8.0.13, OCFS2 1.4.1-1.
>> The shared data partition is 187G, 30 of which used.
>>
>> What would be the lowest needed bandwidth for DRBD to work correctly?
>> Actually we have around 200/400kB, but we experience very slow
>> operations on the filesystem, like for normal directory listing or rsync
>> backups. In OCFS2 they told me it could be a bandwidth problem, partly
>> due to FS and partly to the block device. What are DRBD's minimum
>> requirements?
>>
>> Thank you.
>> -- 
>> Lorenzo Milesi - lorenzo.milesi at yetopen.it
>>
>> YetOpen S.r.l. - http://www.yetopen.it/
>> C.so E. Filiberto, 74 23900 Lecco - ITALY -
>> Tel 0341 220 205 - Fax 178 607 8199
>>
>> GPG/PGP Key-Id: 0xE704E230 - http://keyserver.linux.it
>>
>> -------- D.Lgs. 196/2003 --------
>>
>> Si avverte che tutte le informazioni contenute in questo messaggio sono
>> riservate ed a uso esclusivo del destinatario. Nel caso in cui questo
>> messaggio Le fosse pervenuto per errore, La invitiamo ad eliminarlo
>> senza copiarlo, a non inoltrarlo a terzi e ad avvertirci non appena
>> possibile.
>> Grazie.
>>
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>>
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-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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