How does Voldemort compare to Cassandra?

How does Voldemort compare to Cassandra?

I'm not talking about size of community and only want to hear from people who have actually used both.

Especially I'm interested in:

• How they dynamically scale when adding and removing nodes
• Query performance
• How they scale when adding nodes (linear)?
• Write speed

Voldemort's support for adding nodes was just added recently (this month). So I would expect Cassandra's to be more robust given the longer time to cook and a larger community testing.

Both are fast (> 10k ops/s per machine). Because of their storage designs, I would expect Cassandra to be faster at writes, and Voldemort to be faster at reads. I would also expect Cassandra's performance to degrade less as the amount of data per node increases. And of course if you need more than just a key/value data model Cassandra's ColumnFamily model wins.

I don't know of any head-to-head benchmarks since the one done for NoSQL SF last June, which found Cassandra to be somewhat faster at whatever workload mix he was using. (The "vpork" talk from http://blog.oskarsson.nu/2009/06/nosql-debrief.html) 8 months is an eternity with projects under this much development, though.

Some additional comments:

• Regarding write speed, Cassandra should be faster -- it is designed to be faster to write than read (you can avoid immediate disk hit for writes due to specialized way storage is done)

But main difference I think is actually not performance but feature set: Voldemort is strictly a key/value store (currently anyway), whereas Cassandra can offer range queries (with order-preserving partitioner), and bit more structure around data (column families etc). Former is an important consideration for design; latter IMO less so, you can always structure BLOB data on client side.