Re: [Xen-users] GPLPV domu high cpu from System and System Interrupts processes

[Micky <mickylmartin@xxxxxxxxx>]

I believe I have figured it out.

The default value of snapshot_autoextend_threshold in
/etc/lvm/lvm.conf is 100, which just simply disables the automatic
snapshot expansion.
No where in the documentation mentions that.

After modifying both snapshot* values in lvm.conf, you have to
manually kill dmeventd daemon to reread the lvm.conf file, as it gets
restarted when a snapshot is created.

One more important defacto standard, dmevent doesn't instantly expands
the snapshots but rather checks for thresholds every 10 seconds or so.
So, if the domu has high I/O activity, you are better of by setting
the extend value by 50% or similar.

*It is REALLY IMPORTANT to configure to AUTOMATIC SNAPSHOT EXPANSION
because if a snapshot overflows, YOUR BACKUP WILL BE CORRUPT*

On Sun, May 26, 2013 at 5:19 PM, Micky <mickylmartin@xxxxxxxxx> wrote:
> The domu itself is running on a separate lvm. I was just using
> snapshots for backups. Indeed, the snapshot got over flowed with i/o
> errors. Sadly the last backup with lvm seemed to have few gigs more
> than the original size of the lvm so i am gonna have to shit to other
> means to restore it. LOL!
>
>  Pretty weird as it happened when the snapshot got filled in.
>
> Dmeventd should have auto expanded the snapshot according to lvm.conf
> but it didn't. Testing.
>
> On Sun, May 26, 2013 at 4:50 PM, James Harper
> <james.harper@xxxxxxxxxxxxxxxx> wrote:
>>>
>>> Discard that. It appears that lvm snapshot size (the one I'm using for
>>> backups) got exceeded with i/o errors resulting in high DCP latency
>>> from ata.sys driver. Though lvm backups are quite risky but still it
>>> questions the fact that a simple i/o related issue on an lvm based
>>> domu can render it unbootable.
>>>
>>
>> If the snapshot becomes full then it becomes disabled. Are you running your 
>> domu on the snapshot itself or are you just saying that there is a snapshot 
>> and it got full?
>>
>> James

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