I'm moving over to Linux when the new SSD arrives. SSD gives increased performance, so I thought that I could encrypt everything.
No. An empty block will still be listed as empty and thus be TRIMed.
Even if your drive is encrypted, the drive itself knows nothing of the encryption, just where which data is (and which space isn't used at the moment). So it'll be fine.
As for the performance, I don't know how the impact might be. It would seem that certain optimizations in the SSD might not work, but I cannot figure which ones require knowledge about the actual data so there will probably be no impact from a storage point of view.
Note that encryption requires extra CPU cycles, so the impact might be noticeable there.
man 5 crypttab:
Allow using of discards (TRIM) requests for device.
WARNING: Assess the specific security risks carefully before enabling this option. For example, allowing discards on encrypted devices may lead to the leak of information about the ciphertext device (filesystem type, used space etc.) if the discarded blocks can be located easily on the device later.
Kernel version 3.1 or more recent is required. For older versions is the option ignored.
Most of the tutorials I've read about setting up LUKS drives ask you to
badblocks the entire drive with random data first. This way an attacker cannot know which sectors contain data and which ones haven't been used yet. This information could be used to discover things about the data and correlate with other time-based information which could lead to a compromise.
So, even if the LUKS modules supported sending groups of unused blocks to TRIM, you wouldn't want to do it anyway.
Yes for the latest Fedora 17 with test updates