Re: SSD mystery deepens


root a écrit :

1. Immediately after buying the drive and installing it.
no OS, no FS speed= 475MB/s
2. After partitioning into 2 120GB partitions and installing
an ext4 system with my OS speed=318 MB/s
3. After re-partitioning with 1 240GB partition, ext4 FS,
and my OS speed=228MB/s
In preparation for returning the drive I nulled out
the drive with:
dd if=/dev/zero of=/dev/sdb (I had switched the drive to sdb).

4. After zeroing out the entire drive I ran another speed test
and found speed=386MB/s
5. Encouraged I put an ext4 FS but no OS: speed=479MB/s

6. Wow, I was back in business, so this time I re-installed
the OS and was back to speed=228MB/s

I am completely baffled by these results. Anyone with the
slightest idea of what is happening?

Of course I may be wrong, but all this seems to confirm my theory that
the disk controller knows when blocks do not contain data and do not
actually read from them. So the actual read speed of actual data (which
is what matters, there is no point in reading blocks that do not contain
data) seems to be 228 MB/s.