[Gluster-users] To RAID or not to RAID...

[Markus Kern]

Hi Strahil,

thanks for you answer - but now I am completely lost :)

 From this documentation:
https://docs.oracle.com/cd/E52668_01/F10040/html/gluster-312-volume-distr-disp.html

"As a dispersed volume must have a minimum of three bricks, a 
distributed dispersed volume must have at least six bricks. For example, 
six nodes with one brick, or three nodes with two bricks on each node 
are needed for this volume type."

So for a distributed dispersed volume I need at least six bricks. If 
each brick is a RAID6, I have 6 x 2 Parity disks = 12 disks for parity.

In your example you only have one brick per node in a three node setup. 
This is no distributed dispersed volume then, right?

A confused Markus


Am 14.01.2020 16:29, schrieb Strahil:
> Hi Markus,
> 
> Distributed dispersed volume is just LVM's linear LV -> so in case of
> brick failiure - you loose the data on it.
> 
> Raid 6 requires  2 disks  for parity, so you can make a large RAID6
> and use that as a single brick - so the disks that hold  the parity
> data are  only 6 ( 3 nodes x 2 disks).
> 
> Of course  if you have too many disks  for a single raid controller
> ,that you can consider a  replica volume  with an arbiter.
> 
> 
> Best Regards,
> Strahil Nikolov
> 
> On Jan 14, 2020 13:36, Markus Kern <gluster at military.de> wrote:
>> 
>> 
>> Greetings again!
>> 
>> After reading RedHat documentation regarding optimizing Gluster 
>> storage
>> another question comes to my mind:
>> 
>> Let's presume that I want to go the distributed dispersed volume way.
>> Three nodes which two bricks each.
>> According to RedHat's recommendation, I should use RAID6 as underlying
>> RAID for my planned workload.
>> I am frightened by that "waste" of disks in such a case:
>> When each brick is a RAID6, I would "loose" two disks per brick - 12
>> lossed disks in total.
>> In addition to this, distributed dispersed volume adds another layer 
>> of
>> lossed disk space.
>> 
>> Am I wrong here? Maybe I didn't understand the recommendations wrong?
>> 
>> Markus
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