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

[Strahil]

Hi Markus,


You are right  .I think that the 3 node setup matches distributed volume.

According to https://docs.gluster.org/en/latest/Administrator%20Guide/Setting%20Up%20Volumes/

Dispersed  volumes  use erasure codes to have a 'parity' on a separate brick. In such case you can afford to  loose a brick without loosing data and you will need more bricks.

Yet, I don't see anything about RAID6 being required.

Use the gluster's official documentation (if possible) as it is the most recent info.

Maybe you can share the ammount of disks , raid controllers and servers you have and your tolerance to data loss. Then I can share my thoughts on the possible volume types.

Best Regards,
Strahil Nikolov

On Jan 14, 2020 20:33, Markus Kern <gluster at military.de> wrote:
>
> 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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