My hard drive is a SanDisk SSD. The drive is new. I've booted into ArchLinux Live System, with the intention of preparing the hard drive for full disk encryption. I've noticed a significant drop of write speed over time, see image:


The same issue can also be observed when dd'ing directly from /dev/zero to /dev/sda.

Is this a usual behavior when dd'ing SSDs? Is there a wrong setting in the configuration/BIOS? Or is the SSD broken?


While some performance loss is to be expected when filling an SSD entirely with random data, I don't know what's going on with your particular model.

The blocksize you chose for dd is far too large; but I'd be suprised if it was the cause of performance drops as severe as you're seeing.

Will you be using TRIM (cryptsetup --allow-discards)? If so, it's pointless to overwrite it like this, and the only preparation you need is blkdiscard. In most encryption setups, the real security issues are elsewhere. Here's what a encrypted&trimmed SSD looks like.

  • I doubt that 16MB would be far from optimal for the block size. Anyway a block size that's too high only really hurts when both input and output are doing I/O (or when the block size gets to be a sizable fraction of RAM), which isn't the case here. Mar 4 '15 at 23:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.