RAID 5 disks not spinning down

RAID 5 disks not spinning down

[Alexander Stockinger]

Hi all,

I have a linux software RAID 5 running on a Debian Sarge with 2.6.7-smp. 
Since I installed the system (several kernel updates ago) the disks of 
the RAID 5 won't stay spinned down. Having them sent to standy manually 
using hdparm ends up in having the disks spin up within the next minute 
or so.
To further investigate the problem I watched the /proc/diskstats file 
for /dev/md0 and realized that prior to the spinup a single read access 
to the RAID is issued - consequently the disks attached to the read spin 
up again...
In order to find the reason for that read I did a dnotify on the mount 
point of the RAID - however this didn't show ANY file read at all when 
this single read access occurs.
I also tried noflushd - it simply keeps segfaulting after a few seconds. 
Plus I'd be happy to resolve the issue in the first place instead of 
fixing the symptoms anyway...

Any ideas what to do?

Thanks,
Alex

Re: RAID 5 disks not spinning down

[Brad Campbell]

Alexander Stockinger wrote:
> Hi all,
> 
> I have a linux software RAID 5 running on a Debian Sarge with 2.6.7-smp. 
> Since I installed the system (several kernel updates ago) the disks of 
> the RAID 5 won't stay spinned down. Having them sent to standy manually 
> using hdparm ends up in having the disks spin up within the next minute 
> or so.
> To further investigate the problem I watched the /proc/diskstats file 
> for /dev/md0 and realized that prior to the spinup a single read access 
> to the RAID is issued - consequently the disks attached to the read spin 
> up again...

Does it occur if you have the filesystem on the md device unmounted?

Regards,
Brad
-- 
"Human beings, who are almost unique in having the ability
to learn from the experience of others, are also remarkable
for their apparent disinclination to do so." -- Douglas Adams

Re: RAID 5 disks not spinning down

[Alexander Stockinger]

Brad Campbell wrote:
> Alexander Stockinger wrote:
> 
>> Hi all,
>>
>> I have a linux software RAID 5 running on a Debian Sarge with 
>> 2.6.7-smp. Since I installed the system (several kernel updates ago) 
>> the disks of the RAID 5 won't stay spinned down. Having them sent to 
>> standy manually using hdparm ends up in having the disks spin up 
>> within the next minute or so.
>> To further investigate the problem I watched the /proc/diskstats file 
>> for /dev/md0 and realized that prior to the spinup a single read 
>> access to the RAID is issued - consequently the disks attached to the 
>> read spin up again...
> 
> 
> Does it occur if you have the filesystem on the md device unmounted?

No, drives stay down when the mount point of /dev/md0 is unmounted. So 
it's probably an application accessing something on the disks? But how 
do I determine what is accessed? dnotify reports _nothing_...

> 
> Regards,
> Brad

Thanks,
Alex