What is the maximum value size you can store in redis?

All string values are limited to 512 MiB. This is the size limit you probably care most about.

EDIT: Because keys in Redis are strings, the maximum key size is 512 MiB. The maximum number of keys is 2^32 - 1 = 4,294,967,295.

Values, on the other hand, can vary in size depending on their type. For aggregate data types (i.e. hash, list, set, and sorted set), the maximum value size is 512 MiB for each element, although the data structure itself can have up to 2^32 - 1 elements.

https://redis.io/topics/data-types

https://redis.io/topics/faq#what-is-the-maximum-number-of-keys-a-single-redis-instance-can-hold-and-what-is-the-max-number-of-elements-in-a-hash-list-set-sorted-set

http://groups.google.com/group/redis-db/browse_thread/thread/1c7e33fbc98734b3?fwc=2

Article about Redis Memory Usage can help you to roughly determine how much memory your database would take.

It's in the order of the amount of RAM you have, at least, so unless you plan on puting multi-gigabyte objects in there I wouldn't worry. I've had sets that were hundreds of megabytes big without a problem, but I don't know the exact limits.