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At a minimum, you want 100 partitions per disk.  More partitions doesn't
really matter unless you get way too many (for example 100K partitions on a
disk is probably a bad idea).  And yes, since there are 3 replicas, there
will be 3 copies of every partition.

When determining the part power, you really want to think about what the
max size of your cluster in terms of disk might be, and calculate how many
partitions you need based on that, not how many disks you have now.

I have a google spreadsheet that can help determine what part size to use:

https://docs.google.com/spreadsheet/ccc?key=0At4SyQdtaLTjdGp6R0ZiNnhYQV9WUDJFcllHODJJZFE&usp=sharing

Changing the parameters will show you what the max size a cluster can be
based on the chosen partition size.

--
Chuck


On Fri, Sep 6, 2013 at 3:45 AM, Vil Surkin <vill.srk at gmail.com> wrote:

>  In source code (
> https://github.com/openstack/swift/blob/master/bin/swift-ring-builderline 289) i found, that partitions count multiple 'replica_count' param
> only when i print information about ring. So, what 'partition_power' i
> should use for installation with, for example, 500 disks? And how much
> partitions are really placed on disks: 2^part_power or
> 2^port_power*replica_count ?
>
> пятница, 6 сентября 2013 г. в 11:22, Vil Surkin написал:
>
>  Hello,
>
> When i create ring, i use formula like "disks_numbers * 100 and round to
> nearest power of two". I calculate param "part_power" to be near 100 on
> each disk. But when i add devices to ring and rebalance them, then i get
> number of partitions multiplied to "replica_count" number.
>
> So, how much partitions should be on one disk?
>
>
>
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