Multiple disks

Joseph Blomstedt Joseph.Blomstedt at gmail.com
Tue Mar 22 03:47:04 EDT 2011


Oh, I just realized that was only a partial solution to the problem. I
forgot to commit related logic that handles selecting the same
directory on vnode restart. That's what I get for sending out code
late at night. You'll want to maintain a partition->directory index
somewhere to really make it work (or search all directories for an
existing bitcask corresponding to the partition).

For what it's worth, my experiments a few months back in this area
just used a deterministic function to map partitions to a directory.
That's another approach.

-Joe

On Tue, Mar 22, 2011 at 1:25 AM, Joseph Blomstedt
<Joseph.Blomstedt at gmail.com> wrote:
> Each vnode already opens a separate bitcask, therefore there isn't any
> necessary factor preventing the desired behavior. It's just not coded
> that way. While an individual bitcask must be a single directory,
> there is no reason all vnodes need to open bitcasks within a shared
> root directory.
>
> Luckily, it's easy to change this behavior. In fact, I played around
> with the idea awhile back. This question prompted me to find/release
> the code:
> https://github.com/jtuple/riak_kv/commit/a8ab33224651e6850aed385e4c05c1993916a3e5
>
> That commit should apply against riak-0.14.1. It extends the bitcask
> data_root config option to allow for multiple root paths as well as a
> selection strategy (random or spread). Random just randomly chooses
> one of the directories. Spread picks the directory containing the
> fewest already-opened bitcasks -- although, this is a soft guarantee
> since no effort is taken to address multiple vnodes choosing a
> directory concurrently.
>
> Using paths that correspond to different mounted drives should do the trick.
>
> -Joe
>
>
> On Mon, Mar 21, 2011 at 5:29 PM, Greg Nelson <grourk at dropcam.com> wrote:
>> Hello,
>> We are currently evaluating Riak for an application that will store large
>> amounts of data in a write-heavy pattern.  We'd like to pack many disks into
>> each machine.  Currently, it appears that Bitcask uses exactly one directory
>> to store data.  What is the best way to have it use multiple disks?  Is this
>> something Innostore would handle better?
>> We'd like to avoid RAID since we'll be paying for redundancy at a higher
>> level with Riak (N=3, etc.).
>> We'd also like to avoid a JBOD type setup where a single disk failure brings
>> the whole node down, as we'll obviously be increasing those odds with each
>> disk.
>> What I'm wondering is, can each node distribute its vnodes across many
>> disks?  And if one of those disks fails, will Riak handle that appropriately
>> (i.e., the other vnodes continue to operate normally and hand-off data when
>> the new disk comes online)?
>> Thanks!
>> Greg
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>>
>>
>




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