[DRBD-user] DRBD write after write (cache)

ionral daniele.nuzzo at email.it
Wed Feb 9 12:21:35 CET 2011

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




Felix Frank-2 wrote:
> 
> Hi.
> 
>> if I check the status of drbd the following response is: 
>> 
>>  0: cs: Connected ro: Primary / Primary ds: UpToDate / UpToDate C r ---- 
>>     ns: 640864680 nr: 135234784 dw: 776099464 dr: 1520599328 al: 836478
>> bm:
>> 2185 lo: 0 pe: 0 ua: 0 ap: 0 ep: 1 wo: b OOS: 0 
>> 
>> I do not know if it is positive that the method is to write after is
>> Barrier
>> .... reading the manuals of drbd I noticed that in these cases (BBU)
>> performance would be better for a wo:n 
>> 
>> What do you think? 
> 
>>>Possibly? You may want to just test the performance difference.
> 
> so there is no certainty that it is more powerful
> I can just do a test
> 
>> more to this I can tell you that another hardware configuration with a
>> simple SATA disks in software raid  0 configuration (sda and sdb) and
>> without drbd.conf options: no-disk-flushes -no-md-flushes, The drbd uses
>> instead the drain ... that seems to be dangerous without a BBU, but the
>> drbd
>> has preferred this choice, and not clear to me ...
> 
>>>Check you kernel logs. DRBD may have noticed that barriers are not
>>>available for your backing device and thus falls back to drain. Is LVM
>>>involved in your that setup per chance?
> 
>>>Regards,
>>>Felix
> 
> Unfortunately I have nothing in the logs, the rotate deleted the old log,
> but do not understand much because the drbd not find in my backing storage 
> support for the barrier, I use LVM on top of drbd and not vice versa, is
> not this strange thing?
> 
> 
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