My bad, my script has the wrong access order
set `cat $sys/sync_action $sys/mismatch_cnt $sys/sync_completed`
mismatch_cnt should be fetched last.
cheers
Eyal
On 02/13/11 15:32, NeilBrown wrote:
On Sun, 13 Feb 2011 11:01:43 +1100 Eyal Lebedinsky<eyal@xxxxxxxxxxxxxx>
wrote:
I have scripts that do a raid check, then proceed to identify any files
affected. I then manually deal with these.
I have a few issues with this RADI6 setup, here is one.
I am setting sync_min and sync_max, start a check and wait for sync_completed
to equal sync_max.
I assumed that when equal it means that this address was "completed". After
doing this for a while I observed that this is probably not the case.
My expectation is that sync_completed has 'none' until it finished a chunk.
It then updates it with later completed ones. When it reaches sync_max
it pauses, and I then raise sync_max for the next area. This way I can
tell where a mismatch occurs. If sync_completed is set before a chunk
is completed then I may fetch mismatch_cnt too early (while the last
chunk is still being checked). This seems to be the case.
Q: Is this the case?
The intention of sync_completed is that it is only updated after
sync/check/repair/recovery has actually completed to that point. It may be
updated well *after* the sync has happened, but should never be updated
*before*.
However it is entirely possible that the code is not 100% correct.
If you give me details of what you are seeing together with precise kernel
version number I can try to explain them for you.
Setting ranges that are too small (minimum is 1024) makes the check
*very* slow. I notice that ranges of 1m or even 4m are required to
get the check to move along close to the maximum speed.
Q: Does the check take time to speed up rather than immediately go at
the nominated sync_speed_max rate?
This is almost certainly an artifact of the way disk drives work.
To get streaming reads from a disk drive you need to request at least a whole
cylinder at a time. As cylinders differ in size, it really only works if you
request multiple cylinders at a time.
I don't know how big cylinders are these days but I suspect they are a few
hundred K to a Meg. So needing 4M at a time to get streaming happening
doesn't surprise me at all.
NeilBrown
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Eyal Lebedinsky (eyal@xxxxxxxxxxxxxx)
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