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From Alexandre Fouché <afou...@onfocus.io>
Subject stripes, JBOD: Assignment and rebalance ?
Date Thu, 02 Mar 2017 17:18:59 GMT
Hi,

>From the FAQ documentation:

> Kudu handles striping across JBOD mount points, and does not require
RAID. Kudu’s write-ahead logs (WALs) can be stored on separate locations
from the data files

which raises to me a few questions

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 ?

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 found comments that WAL can only be one one disk, is it still the case,
or is this info obsolete ?

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