Regarding temporary "pauses", perhaps due to using an SD card with an XO

Mikus Grinbergs mikus at
Sat Oct 13 15:46:21 EDT 2012

Lately there has been discussion about using an SD card to expand the 
"storage" capability of the XO.  [For instance, discussion of when an XO 
functions as a server, having it keep its database on an SD card.]

What I want to mention is that I experience occasional "pauses" on my XO 
systems (each has a "permanent" SD card, on which I keep Activities, 
Linux executables, etc.).  I do not know what causes these "pauses", but 
my best guess is the following (particularly since "pauses" often occur 
during a CLI command that is "massively" accessing the SD card).

My guess:   SD cards have an "embedded chip" which is responsible for 
"wear levelling" the electronic components used to keep the data.  It 
does this by internally 'rearranging' "which data block is physically 
kept where".  I think this 'rearranging' action by the "embedded chip" 
gets launched (when some 'internal' SD card thresholds are met) during 
an I/O access by the (XO) host -- and this "rearranging" results in that 
host's I/O access being DELAYED until the "embedded chip" is done.

I have not compared the "performance" (from the user's point of view) of 
running an Activity "from the SD card" vs. running it "from the XO".
But I do have the impression that the duration of the occasional 
"pauses" which I as a user notice while running "with the SD card" have 
gotten LONGER as my XOs have migrated to using ever-larger SD cards.


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