Multiple disks

Alexander Sicular siculars at gmail.com
Mon Mar 21 19:51:59 EDT 2011


In short, no. Vnodes can not be pointed to individual disks. Whichever  
backend you use for riak, all the files will live in one directory.

Your only option is raid and to select the raid that is appropriate  
for your application. You basically have 3 options when it comes to  
raid levels:

Striped (raid 0)

Mirrored (raid 1)

Striped + Parity (raid 5)

There are all sorts of extra/other raid levels but those 3 are the  
basic and virtually all hardware raid solutions will offer them. The  
other more exotic ones depend on the raid card.

My recommendation to people who don't know any better or don't care is  
to just use raid 5 and forget about it. Possibly raid 5 + hot spare  
(again depending on card support).

The one thing I do recommend on top of that is to align your chunk or  
block size with the chunk/block size options of your file system and  
to make them large if you are dedicating disk specifically for  
database usage. A block size of 64KB or even 128KB would not be  
outrageous.

Of course, a lot of this is moot if you are using a virtual machine  
service.

Cheers, Alexander


@siculars on twitter
http://siculars.posterous.com

Sent from my iPhone

On Mar 21, 2011, at 16:29, 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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