Individual tablets aren't assigned to a specific disk, they are spread across all of the data disks. So individual disks should fill up evenly.
- Dan On Thu, Mar 2, 2017 at 9:38 AM, Alexandre Fouché <[email protected]> wrote: > Hi Dan > So will Kudu rebalance tablets on different disks dynamically when some > gets bigger than other, in order not to fill a disk while the other disk > space could remain mostly free ? > > 2017-03-02 18:26 GMT+01:00 Dan Burkert <[email protected]>: > >> Hi Alexandre, >> >> responses inline >> >> On Thu, Mar 2, 2017 at 9:18 AM, Alexandre Fouché <[email protected]> >> wrote: >>> >>> >>> When storing data on multiple JBOD disks, will Kudu assign data for >>> tablets efficiently as far as tablet sizes or activity are concerned, or >>> will it simply try to assign roughly the same number of tablets on each >>> disk, regarless of tablets true size or activity (we have many empty >>> tablets at this time). And will it rebalance tablets to one disk or another >>> automatically ? Or is it still better to expose one RAID0 volume ? >>> >> >> Kudu will evenly spread data from all tablets across all disks. This >> allows Kudu to get good write throughput and balancing, but similarly to >> RAID 0 it means that if one drive fails, all tablets on that tablet server >> will become unavailable. Kudu will automatically recover by re-replicating >> the tablets to a different tablet server as long as a majority of replicas >> are still available. So, RAID 0 should provide no benefit for Kudu. It's >> on the roadmap to make multi-disk configuration more flexible so that if a >> single disk dies only a subset of the tablets will become unavailable, but >> I don't have a timeline on that feature (no one is working on it to my >> knowledge). >> >> >>> Will using JBOD disks better than RAID stripes ? It seems from Bug >>> reports that when WAL disk fails, or one of the JBOD data disks, Kudu is >>> still unable to recover and keep or migrate good tablets. In that case, it >>> shows no improvement over a failed disk on a RAID0 where in both cases the >>> only recover option is to delete the whole Kudu data and WAL and let it >>> resync from other nodes ? >>> >> >> I think what I wrote previously answers this, if not I can clarify. >> >> I found comments that WAL can only be one one disk, is it still the case, >>> or is this info obsolete ? >>> >> >> This is currently the case. If you have many disks it's often >> advantageous to put the WAL on it's own disk (ideally an SSD if it's >> available). The WAL workload is more latency sensitive than the data >> workload. >> >> - Dan >> > >
