Basically I am +1 on having both metrics, both can be useful for setting up custom
alerts.
But I am concerned that the percentage based metric is not proper for alerting because of
its relative nature. While it make sense when calculating the heap size based alerts, it
is different in disk space, because differences in partition sizes could be enormous.
"Calculated.SystemDiskSpaceUsedPercentage > 90%" may mean many things on
different HW. I know that the alerts are adjustable and one could change the number to
whatever she wants, but we should provide smart defaults.
What about having another one called for instance
"Calculated.SystemDiskSpaceAvailable" that would be calculated as the sum of
free spaces across all partitions where data dirs for C* are located? (because of the way
how C* selects the data dir) And trigger the alert if the number is lower than X, where X
could be the number of megabytes necessary for storing the data for, say, 7 days. Using
this approach, we could have alert notifications saying something like "If you
don't add more disks, you will run out of space in approx 1 week.".
jk
----- Original Message -----
From: "Jay Shaughnessy" <jshaughn(a)redhat.com>
To: rhq-devel(a)lists.fedorahosted.org
Sent: Monday, July 15, 2013 11:24:00 PM
Subject: Re: Storage Node - Disk Space Metric
On 7/15/2013 4:46 PM, Stefan Negrea wrote:
>
> ----- Original Message -----
>> From: "Jay Shaughnessy" <jshaughn(a)redhat.com>
>> To: rhq-devel(a)lists.fedorahosted.org
>> Sent: Monday, July 15, 2013 11:34:51 AM
>> Subject: Re: Storage Node - Disk Space Metric
>>> 1) Should we include both metrics? Overall disk space use & data files
>>> disk
>>> space used? We could only hope that having the two metrics will make it
>>> easier for users to understand what they are.
>> I think two metrics is a good idea. We must have a way to easily alert
>> on a disk space consumption. The Iteration-3
>> Calculated.PartitionDiskSpaceUsedPercentage metric is useful
>> information: How much of my used disk space is due to my storage node?
>> But it's mainly useful to help understand if a disk space issue is or is
>> not due to the storage node. We need the Iteration-3
>> Calculated.PartitionDiskSpaceUsedPercentage metric for alerting on
>> excessive disk space for the storage node partitions. Of course we'd
>> need two names that describe the distinction. I think both metrics
>> should be on the same resource as they are related.
>>
> If we put the two metrics on the same resource (Cassandra Storage Service)
> how could we prevent confusion over the meaning of the two metrics?
>
> How about these two names: Calculated.DataDiskSpaceUsedPercentage &
> Calculated.SystemDiskSpaceUsedPercentage
Those names aren't bad. I think the descriptions will be important.
Making sure to point out that 'SystemDiskSpaceUsedPercentage' represents
the file system for which data is being written and is equal to (
'DataDiskSpaceUsedPercentage' + non-storage node data).
>
>
> Thank you,
> Stefan Negrea
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