Disk I/O as a bottleneck?

[guy keren]

On Sun, 2011-05-08 at 09:57 +0300, shimi wrote:
> On Sun, May 8, 2011 at 7:28 AM, Nadav Har'El <nyh at math.technion.ac.il>
> wrote:
>         
>         Instead of buying a huge SSD for "thousands of dollars"
>         another option you
>         might consider is to buy a relatively small SSD with just
>         enough space to
>         hold your "/" partition and swap space. Even 20 G may be
>         enough.
>         The rest of your disk - holding your source code, photos,
>         songs, movies,
>         or whatever you typically fill a terabyte with, will be a
>         normal, cheap,
>         hard disk.
>         
>         Several of my friends have gone with such a setup on their
>         latest computer,
>         and they are very pleased.
>         
> 
> I have set up my latest system just like that. Though mine was a bit
> pricey: I went for the Intel X25-E 32GB. The OS and homedir are on it;
> Large datasets go on various Samsung SpinPoint 1TB F3 drives I've
> installed as well. The system is already more than a year old, and the
> free space is < 20%, which, I am assuming, means I've already filled
> the disk (due to deletes and the SSD wear-leveling algorithms) and
> already doing erases, and....the performance is still nothing short of
> AMAZING - sub-1ms seek time is a great thing when you scan the
> filesystem etc.
> 
> It just feels as if Disk I/O is no longer my bottleneck (and the CPU
> is a Quad Core AMD PhenomII 955 with 8GB RAM...). Of course - I don't
> use swap.
> 
> Performance after > 1 year as mentioned:
> # hdparm -t /dev/sda
> 
> /dev/sda:
>  Timing buffered disk reads: 722 MB in  3.00 seconds = 240.27 MB/sec
> 
> As always, YMMV :)

what tends to get worse after the SSD becomes full is writes, not reads.
and combinations of reads and writes make things look worse (the writes
slow down the reads).

however, if you feel that the system is very fast after one year of use
- that's good enough for me.

do you have the ability to extract wear leveling information from your
SSD? it would be interesting to know whether the drive is being used in
a manner that will indeed comply with the life-time expentency it is
sold with (5 years?), or better, or worse.

--guy