Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Thu, 29 May 2008 22:45:48 -0700 Tim Nufire wrote: > Hello, > > The thread "drbd8 and 80+ 1TB mirrors/cluster, can it be done?" > suggests using RAID5 or RAID6 on top of DRBD to improve redundancy... > A distributed RAID 15/16 :-) > No, what people were suggesting was to have RAID5 (or really RAID6 if you use more than 20 or so drives per RAID) native with MD per node and DRBD on top of that. Again, the idea is to improve reliability _locally_ first, step by step. And as far as I know DRBD _always_ has to sit on TOP of the IO layer, be it the actual disk or MD/LVM. > I like this idea so I tried to build it in VMware but I can't get the > RAID5 array to assemble on the mirrored node :-/ I hope I'm missing > something basic but I could not find any documentation on the web > about this. My best guess is that drbd is not synchronizing the RAID > super blocks but I don't know how to change this... I know I can flip > this setup and use DRBD to mirror a RAID5 array but I would rather > mirror first improved reliability and better re-sync characteristics... > You are _not_ improving reliability with many RAID1s. In your setup with 160 total drives statistics and good ole Murphy's law will see to it that 2 drives fail at the same time (or at least before you can replace and re-sync). The setup (RAID6 with several spares) suggested in the previous thread would be such that you never have to re-sync on the DRBD level except for a total node failure. In your configuration with all those DRBD RAID1s you would nearly constantly have some drives gone bad and in "DETACH"ed mode, thus resulting in very much reduced read speed. And with the above mentioned risk factor. Regards, Christian -- Christian Balzer Network/Systems Engineer NOC chibi at gol.com Global OnLine Japan/Fusion Network Services http://www.gol.com/