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From Adar Lieber-Dembo <a...@cloudera.com>
Subject Re: Recommended maximum amount of stored data per tablet server
Date Thu, 02 Aug 2018 18:17:26 GMT
The 8TB limit isn't a hard one, it's just a reflection of the scale
that Kudu developers commonly test. Beyond 8TB we can't vouch for
Kudu's stability and performance. For example, we know that as the
amount of on-disk data grows, node restart times get longer and longer
(see KUDU-2014 for some ideas on how to improve that). Furthermore, as
tablets accrue more data blocks, their superblocks become larger,
raising the minimum amount of I/O for any operation that rewrites a
superblock (such as a flush or compaction). Lastly, the tablet copy
protocol used in rereplication tries to copy the entire superblock in
one RPC message; if the superblock is too large, it'll run up against
the default 50 MB RPC transfer size (see src/kudu/rpc/transfer.cc).

These examples are just off the top of my head; there may be others
lurking. So this goes back to what I led with: beyond the recommended
limit we aren't quite sure how Kudu's performance and stability are
affected.

All that said, you're welcome to try it out and report back with your findings.


On Thu, Aug 2, 2018 at 7:23 AM Quanlong Huang <huang_quanlong@126.com> wrote:
>
> Hi all,
>
> In the document of "Known Issues and Limitations", it's recommended that "maximum amount
of stored data, post-replication and post-compression, per tablet server is 8TB". How is the
8TB calculated?
>
> We have some machines each with 15 * 4TB spinning disk drives and 256GB RAM, 48 cpu cores.
Does it mean the other 52(= 15 * 4 - 8) TB space is recommended to leave for other systems?
We prefer to make the machine dedicated to Kudu. Can tablet server leverage the whole space
efficiently?
>
> Thanks,
> Quanlong

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