On 31/12/2013 00:39, Stan Hoeppner wrote:
On 12/30/2013 2:36 AM, Pieter De Wit wrote:
On 30/12/2013 20:25, Stan Hoeppner wrote:
On 12/29/2013 5:16 PM, Pieter De Wit wrote:
<snip>
Should that resync not have had more completed ?
Your question is invalid. What you meant to ask is
"Why are pvdisplay and mdstat reporting what seems to be conflicting
state data?"
Did you also ask on the lvm list why pvdisplay says most PEs are
consumed, yet mdstat says resync is only 17% complete?
Hi again Stan,
pvdisplay says most PEs are consumed because I moved that data to the
device. My question, rephased then:
Shouldn't writes to a RAID device count as resyncs ?
The resync process is independent of normal IO. It starts at the
beginning and soldiers on to the end doing a read of each sector pair
then comparing them (for RAID1). So no, writes don't count as resync
operations. md doesn't perform write/read/verify in normal operation,
only write. Linux relies on hardware to report write errors, and
assumes the data hit the disk intact if no error. There is no mechanism
to pass a new write as verified to the resync process. If you think it
should you may want to shoot the idea past Neil. Though I'm sure he's
already considered that and rejected it for various reasons.
And unless you restart the resync, it won't verify any sectors you wrote
up to its current position. Any sectors you wrote after that point it
will be verifying. You don't need to restart the resync or do another
one. I'm simply explaining how the resync is independent of normal
write IO.
Hi Stan,
I will leave the email intact for Neil. Neil, please point out anything
I have missed :)
I understand, but why is the following not the same then (let's stick to
RAID 1 for now, just to make it easier)
* Read both sectors, yip, they are the same
* Write both sectors with the same data, none reported an error
The one outstanding thing I can think of is that this will require a
major re-write of the code. I *assume* that MD doesn't track the resync
progress by bitmap, but rather by sector count.
The second is that it could become hell to update a bitmap if there in
threads involved, I am also guessing it will create havoc for the
scheduler, since a write now has to update the bitmap, but in order to
do so, it needs a memory lock, which means that it might have to wait
for the sync read to complete.
Cheers,
Pieter
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