Re: SSD mystery deepens



root <NoEMail@xxxxxxxx> wrote:
root <NoEMail@xxxxxxxx> wrote:
All speed tests mentioned here come from hdparm -t /dev/sda

In an earlier post I wondered about the decreasing performance
of my 240GB Corsair F3 SSD. Some useful suggestions were
given about changes to be made in /etc/fstab to ensure
best performance and longer life for the SSD. Among others,
these suggestions include noatime, discard, nodiratime.


I also read the Wikipedia article on SSD which mentioned
TRIM. I made the changes suggested and rebooted my system.
The Wiki article suggested that it is not good to have
your SSD run near capacity. I had partitioned the drive
into two partitions of 120GB each. So, I used gdisk
(previously I used fdisk) to wipe the partition information
and create a new 240GB partition (really 227GB).
I re-installed my OS and found a 35% speed degradation.

Here is a summary of my experience.

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

At this point I decided to return the drive, each install
of the OS caused about a 33% reduction in the speed

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?

I have sent email to Corsair but I don't expect anything
from that.

The results are somewhat repeatable, except that I am
unable to regain the 318MB/s speed that first obtained.

The 228MB/s speed holds whether I use fdisk or gdisk
to partition the drive, and whether the drive is
partitioned as a single 240GB partition or 2 120GB
partitions.


I think I understand what the problem is: the hdparm test
doesn't mean anything. I just ran a real test that involved
lots of real disk i/o. The results with my sata3 spinning
disk took 15m 16s. The same test, with the same data
on the ssd took 4m 4s. So the ssd is at least 3.75
as fast. I say at least because there was considerable
output to the screen during the test.

I think this will finish me efforts with the ssd. I want
to thank everyone for contributing to the thread.
.