[DRBD-user] Disk Corruption = DRBD Failure?

Charles Kozler charles at fixflyer.com
Wed Oct 12 20:30:43 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.


I will re-read the DRBD Funadmentals- the way I understood it was 
basically if you were writing to node1 it wouldn't put the data through 
a TCP socket and would actually just write directly to the block device 
and that TCP was usually only used for the actual replicating and data 
integrity conversation between the hosts.  My understanding now is that 
for all hosts included in the resource definition it will put the data 
into that socket - including the host you're writing from (eg: if I 
wrote to /dev/drbd0 on host1 it will go through the socket to write the 
data still to write it to the underlying block device- I had originally 
thought it would skip the TCP socket write and write directly to the 
block device).

I hope that was clear? It probably doesnt make sense because my original 
understanding was wrong :)


Regards,
Chuck Kozler
/Lead Infrastructure & Systems Administrator/
---
*Office*: 1-646-290-6267 | *Mobile*: 1-646-385-3684
FIX Flyer

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On 10/12/2011 2:09 PM, Florian Haas wrote:
> On 2011-10-12 20:00, Charles Kozler wrote:
>> This was 100% spot on the answer I was looking for- thanks guys!
>>
>> Also, do any white papers exist on how DRBD works on the inside? From
>> what you told me it looks like its
> Um, "DRBD Internals" in the DRBD User's Guide? You can also check out
> the Publications sections in that same guide; but those are most likely
> of interest to kernel developers only. But don't let that scare you,
> dive right in if you're so inclined. :)
>
>> Write to DRBD Block Device ->  Write to TCP buffer ->  Write to host disks
>>
>> I thought it was
>>
>> Write DRBD Block Device ->  Write to disk ->  Write to TCP Buffer ->  Write
>> to host disks (like a push method almost)
> So what's the difference between "Write to disk" and "Write
> to host disks" in your model?
>
> The actual pattern is also described in the User's Guide; see the
> chapter named "DRBD Fundamentals".
>
>> Which is why I wanted to know about disk corruption but from what it
>> seems like is that I should be more concerned about corruption in the
>> network stack, right?
> No you should be concerned about both, because your users will eat you
> alive if you present them broken data, no matter the source of breakage.
>
> Cheers,
> Florian
>
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