Re: RAID halting

[Roger Heflin <rogerheflin@gmail.com>]

Lelsie Rhorer wrote:
>> This sounds like a filesys problem rather than a RAID problem.
> 
> I considered that.  It may well be.
> 
>> One thing that can cause this sort of behaviour is if the filesystem is in
>> the middle of a sync and has to complete it before the create can
>> complete, and the sync is writing out many megabytes of data.
> 
> For between 40 seconds and 2 minutes?  The drive subsystem can easily gulp
> down 200 megabytes to 6000 megabytes in that period of time.  What synch
> would be that large?  Secondly, the problem occurs also when there is
> relatively little or no data being written to the array.  Finally, unless I
> am misunderstanding at what layers iostat and atop are reporting the
> traffic, the fact all drive writes invariably fall to dead zero during an
> event and reads on precisely half the drives (and always the same drives)
> drop to dead zero suggests to me this is not the case.
> 
> 

If you have things setup such that you have lights on the disks, and 
can check the lights when the event is happening, often if a single 
drive is being slow it will be the only one with its lights on when 
things are going bad.