Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 02/07/2012 03:16 AM, Felix Frank wrote: > Hi, > > On 02/07/2012 08:36 AM, Jaap78 wrote: >> >> Hello, >> >> Normally DRBD writes changes from device /dev/drbd[x] to a lower level block >> device (for example /dev/sda) and then submit it to the secondary node. >> >> Does DRBD also submit changes to the secondary node, if the change came from >> the lower level block device (/dev/sda)? > > no, it cannot possibly do that. It's crucial that the backing device is > not touched once DRBD is operational. Otherwise you won't ever find out > what blocks have diverged by writing through this "bypass". > >> I am looking for a way to migrate a 8TB SAN to SAN storage server. > > So your idea is to add DRBD metadata to your existing SAN and have any > changes replicated from then on? > > I fear there is no way to do this. You will need a downtime, but it > should be possible to keep it as short as a couple of minutes: > 1. add DRBD as you seem to be planning > 2. shut down your services, unmount > 3. do drbdadm create-md, go primary and bring the drbd up > 4. mount (drbd instead of backing storage) > > Your downtime comprises step 3, and can be done rather quickly (a bit of > practice doesn't hurt for this). > > This way you opt to set up a standalone primary at first. You can then > take your time for setting up the peer. If you need to keep the initial > sync short as well, some more planning is in order, so that ideally you > can do some variation of truck based replication. > > HTH, > Felix To clarify or add a bit to Felix's comments; The meta data requires a certain amount of free space (the exact amount can be calculated using the formula on the DRBD website docs). This will required adding a bit of physical space, if possible, shrinking the FS a certain amount, again if possible, or adding a new disk and configuring external metadata. -- Digimer E-Mail: digimer at alteeve.com Papers and Projects: https://alteeve.com