Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
So, let's assume a raid -> drbd -> lvm starting with a single RAID1, what If I would like to add a second raid1 converting the existing one to a RAID10 ? drbdadm resize would be enoguh ? keeping lvm as the upper layer would be best, I think, because will allow me to create logical volumes, snapshot and so on. what happens if local raid totally fails ? the upper layer will stay up thanks to DRBD fetching data from the other node ? is "raid -> drbd -> lvm" a standard configuration or something bad? I don't want to put in production something "custom" and not supported. How to prevent splitbrains ? Would be enough to bond the cluster network ? Any qdevice or fencing to configure ? 2017-10-11 21:07 GMT+02:00 Adam Goryachev <mailinglists at websitemanagers.com.au>: > > > On 12/10/17 05:10, Gandalf Corvotempesta wrote: >> >> Previously i've asked about DRBDv9+ZFS. >> Let's assume a more "standard" setup with DRBDv8 + mdadm. >> >> What I would like to archieve is a simple redundant SAN. (anything >> preconfigured for this ?) >> >> Which is best, raid1+drbd+lvm or drbd+raid1+lvm? >> >> Any advantage by creating multiple drbd resources ? I think that a >> single DRBD resource is better for administrative point of view. >> >> A simple failover would be enough, I don't need master-master >> configuration. > > In my case, the best option was raid + lvm + drbd > It allows me to use lvm tools to resize each exported resource as required > easily: > lvmextend... > drbdadm resize ... > > However, the main reason was to improve drbd "performance" so that it will > use different counters for each resource instead of a single set of counters > for one massive resource. > > BTW, how would you configure drbd + raid + lvm ? > > If you do DRBD with a raw drive on each machine, then use raid1 on top > within each local machine, then your raw drbd drive dies, the second raid > member will not contain or participate with DRBD anymore, so the whole node > is failed. This only adds DR ability to recover the user data. I would > suggest this should not be a considered configuration at all (unless I'm > awake to early and am overlooking something). > > Actually, assuming machine1 with disk1 + disk2, and machine2 with disk3 + > disk4, I guess you could setup drbd1 between disk1 + disk3, and a drbd2 with > disk2 + disk4, and then create raid on machine 1 with drbd1+drbd2 and raid > on machine2 with drbd1+drbd2 and then use the raid device for lvm. You would > need double the write bandwidth between the two machines. When machine1 is > primary, and a write for the LV, it will be sent to raid which will send the > write to drbd1 and also drbd2. Locally, they are written to disk1 + disk2, > but also those 2 x writes will need to send over the network to machine2, so > it can be written to disk3 (drbd1) and disk4 (drbd2). Still not a sensible > option IMHO. > > The two valid options would be raid + drbd + lvm or raid + lvm + drbd (or > just lvm + drbd if you use lvm to handle the raid as well). > > Regards, > Adam > _______________________________________________ > drbd-user mailing list > drbd-user at lists.linbit.com > http://lists.linbit.com/mailman/listinfo/drbd-user