CentOS - Jul 2009 - mdadm RAID sync speed limitation?

While creating some arrays this evening, I noticed this line my dmesg:

md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec)
for reconstruction.

Why is there a 200MBps limitation on the mdadm sync speed? It certainly
isn't a concern for my particular systems (15k U320 SCSI) but I can imagine
there are much higher end systems that actually could sync at a rate equal to or
higher than the limit. Is this limit arbitrary? Based on detected system specs?
Limitation of mdadm itself?

Just curious.

--Tim

Tim Nelson wrote:
> to or higher than the limit. Is this limit arbitrary? Based on detected
> system specs? Limitation of mdadm itself?
>From the docs..
http://www.mjmwired.net/kernel/Documentation/md.txt

453	   sync_speed_min
454	   sync_speed_max
455	     This are similar to /proc/sys/dev/raid/speed_limit_{min,max}
456	     however they only apply to the particular array.
457	     If no value has been written to these, of if the word 'system'
458	     is written, then the system-wide value is used.  If a value,
459	     in kibibytes-per-second is written, then it is used.
460	     When the files are read, they show the currently active value
461	     followed by "(local)" or "(system)" depending on
whether it is
462	     a locally set or system-wide value.

Much higher end systems probably aren't running software
raid in any case. I can't imagine using it myself for more
than a few disks, the inconvenience alone of having to worry
about keeping boot records intact or manually re-syncing
is enough to keep me on hardware raid, which hasn't really
ever let me down over several hundred controllers over the
past many years(I only use good controllers though).

nate