Disk I/O as a bottleneck?

[geoffrey mendelson]

On May 8, 2011, at 9:30 AM, Yedidyah Bar-David wrote:
>
> I am considering, for my next laptop, and taking into account the fact
> that most laptops do not have space for two disks but do have some  
> kind
> of flash memory slot ("card reader") - usually SD-something, to have  
> the
> OS on a (e.g.) SD card of 16 or 32 GB. I have no other experience with
> such cards, so I do not know if they are considered durable enough,  
> fast
> enough - both random and sequential IO, both compared to SATA  
> mechanical
> disks and to SATA flash ones, etc. Comments are welcome :-)

It depends upon how you do it. The main difference in this case  
between a SOLID STATE DISK and memory card is the number of times you  
can write on it before it stops working.

Modern memory cards do not use the same physical location for data all  
the time. The card itself randomizes where you write data, so that the  
useage of each bit on the card is spread out evenly.

  Of course this only works if the card is not full, and the emptier  
it is the better off you are.
Whether this works with *NIX file systems is another question and I  
can't answer it.

One of the bad things is that standard *NIX files systems are designed  
with magnetic media in mind, they update the access time of files  
every time you open them. This is bad for files that are opened often.

The way around this is to mount a file system read only. Using a  
compressed read only file system, such as that on a "live" CD works  
well in this case. The problem with it is that you can't
add software or change settings.

UBUNTU has a setup where you can install a "live" system to a memory  
card/stick and it will mount your home directory in the unused space.  
If you can live with the limitations, then it will work for you.

I think someone else said to use a small SSD for the system and a hard  
disk for your data. This would work extremely well for this situation  
where instead of a hard disk, you used a memory stick or card for it.

It also depends upon what you are doing with it. Besides  
entertainment, my needs are fullfilled with an Xterm type terminal,  
SSH, a web browser and an email program. For entertainment, an MP3  
player and one that will play 360P videos is enough. This can be  
accomplised with a lower power processor (Intel Atom for example) and  
a small screen.

While you can get laptops with 15 inch screens and I7 processors, I'm  
not sure you would gain anything except a higher price by replacing a  
disk with an SSD/memory card combo.

The latest Apple rumor is that they are going to produce a laptop soon  
with an ARM processor.Based on the success of the iPad, it probably  
will be a netbook size screen, a multicore ARM processor and a  
keyboard. It may or may not have a touch screen.


I'm hoping that this rumor, whether there is any truth to it or not  
will fuel development of small ARM based netbooks. Unfortunately  
netbooks instead of getting smaller and cheaper, have gone the other  
way and become more expensive, larger, heavier and more powerfull.


Geoff.


-- 
Geoffrey S. Mendelson,  N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.