Think of it this way, when you have a normal system, your write is flushed out to the disk as fast as possible. When you add in full disk encryption, you're going to have to encrypt on write. Your write won't be acknowledged until it's physically on the disk, so the faster your disk is, the faster your write will be acknowledged. Same thing with reads, the faster you can read, the sooner you can decrypt and return the data to the application.
So SSD is definitely the way to go if you want to encrypt the whole disk. If that's too expensive, get a 7200rpm laptop drive.
The amount of time and overhead you have when encrypting on write or decrypting on read is the same for an SSD or HDD. So you're adding the same time lag and CPU overhead in either case. Only with an SSD the time lag is a greater proportion of the total time lag. Also, encrypting a sector means that SSD firmware can't compress it, which some would do. The argument you gave just says... that SSD's are faster. That is not news.
Also, the SSD firmware stores much more metadata about access patterns, which could revert your efforts at keeping your doings private.
Comments
Think of it this way, when you have a normal system, your write is flushed out to the disk as fast as possible. When you add in full disk encryption, you're going to have to encrypt on write. Your write won't be acknowledged until it's physically on the disk, so the faster your disk is, the faster your write will be acknowledged. Same thing with reads, the faster you can read, the sooner you can decrypt and return the data to the application.
So SSD is definitely the way to go if you want to encrypt the whole disk. If that's too expensive, get a 7200rpm laptop drive.
The amount of time and overhead you have when encrypting on write or decrypting on read is the same for an SSD or HDD. So you're adding the same time lag and CPU overhead in either case. Only with an SSD the time lag is a greater proportion of the total time lag. Also, encrypting a sector means that SSD firmware can't compress it, which some would do. The argument you gave just says... that SSD's are faster. That is not news.
Also, the SSD firmware stores much more metadata about access patterns, which could revert your efforts at keeping your doings private.