Feeds

Facebook builds 'McDipper' – memcached for flash

Sizzles flash like memcached made DRAM dance

Build a business case: developing custom apps

For some things you need DRAM, but for everything else there's flash.

At least that's the message Facebook gave on Tuesday when it took the wraps off 'McDipper', a technology the social network has developed to let it save on memory and get more out of its flash.

In a post to the Facebook engineering blog that is sure to get the brains of storage nerds revving, the social network's engineering team gave details on its memcache protocol–compatible McDipper flash-based cache server.

"The main design goals of McDipper are to make efficient use of flash storage (i.e. to deliver performance as close to that of the underlying device as possible) and to be a drop-in replacement for Memcached," the team wrote in a post to the blog.

McDipper can be a handy tool for companies looking to minimize their use of expensive RAM without having to compromise on latency.

For example, Facebook has used McDipper in its infrastructure for the past year in such a way the social network can keep hashed metadata about photos in memory, but keep the unwieldy large photos on flash.

McDipper is memcache for flash

McDipper's storage layout

"This configuration gives us the large sequential writes we need to minimize write amplification on the flash device and allows us to serve a photo fetch with one flash storage read and complete a photo store with a single write completed as part of a more efficient bulk operation," the company wrote.

By using McDipper, Facebook has been able to cut the number of servers for some tasks by as much as 90 per cent, while making sure that over 90 per cent of requests are met with responses in the sub-millisecond range.

Though many storage technologies offer a variety of tools for tiering data across storage, these tend to come with either a latency overheard or a wallet-breaking license fee.

Memcached, on the other hand, is a stripped-down, well-understood system that, though limited, lets administrators cut through their infrastructure and talk straight to the storage bones. It turns 10 this year, and was initially developed to support LiveJournal.

By developing McDipper, Facebook has given itself another way of avoiding the pitfalls that come with depending on a specific vendor's technology.

The tech is being used to serve over 150Gbps from forward caches in Facebook's content delivery network (CDN) at the moment, the company wrote in the post.

Though the company has no immediate plans to publish the protocol as open source, the team that developed it would like to, a Facebook spokesman told The Register.

Until then, this peek behind the social network's curtain serves to spin-up storage engineers' imaginations, and perhaps get a few more infrastructure CVs plopping onto the doormat at Zuckerberg HQ. ®

Boost IT visibility and business value

More from The Register

next story
Microsoft: Azure isn't ready for biz-critical apps … yet
Microsoft will move its own IT to the cloud to avoid $200m server bill
Shoot-em-up: Sony Online Entertainment hit by 'large scale DDoS attack'
Games disrupted as firm struggles to control network
Silicon Valley jolted by magnitude 6.1 quake – its biggest in 25 years
Did the earth move for you at VMworld – oh, OK. It just did. A lot
VMware's high-wire balancing act: EVO might drag us ALL down
Get it right, EMC, or there'll be STORAGE CIVIL WAR. Mark my words
Forrester says it's time to give up on physical storage arrays
The physical/virtual storage tipping point may just have arrived
VMware vaporises vCHS hybrid cloud service
AnD yEt mOre cRazy cAps to dEal wIth
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Endpoint data privacy in the cloud is easier than you think
Innovations in encryption and storage resolve issues of data privacy and key requirements for companies to look for in a solution.
Scale data protection with your virtual environment
To scale at the rate of virtualization growth, data protection solutions need to adopt new capabilities and simplify current features.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?