Stand back: I'm going to try science!
Jun. 6th, 2013 05:57 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
sawylHaving considered recent difficulties, I've concluded that most of our problems have been brought on by a lack of date. So, as a good scientist, I've tried to come up with a way to remedy the situation. My solution? To run a series of tests that involve deliberately breaking the data mirror by taking half the logical disks out of service for a fixed period and timing the resynchronisation process.
According to my theory, this ought to show whether the resync time is proportional to the duration of the split — and, by implication assuming a constant load on the file system, the amount of data written during the period — or whether it is dependent on the size of the metadata, which can be assumed to be relatively constant over the period.
If the initial experiment indicates that the time to resynchronise varies with the duration, then it ought to be possible to repeat the tests with gradually increasing intervals and to use the resulting data to create a model. If the resync time appears to be constant, at least within the time frame of the split, then we can be relatively confident that, for short outages at least, we can predict the duration and hence the impact of an outage of the mirror.
While I'm not sure anyone will actually go for this — the impact of the data gathering process may be too sever to tolerate — I think it's worth pitching...
According to my theory, this ought to show whether the resync time is proportional to the duration of the split — and, by implication assuming a constant load on the file system, the amount of data written during the period — or whether it is dependent on the size of the metadata, which can be assumed to be relatively constant over the period.
If the initial experiment indicates that the time to resynchronise varies with the duration, then it ought to be possible to repeat the tests with gradually increasing intervals and to use the resulting data to create a model. If the resync time appears to be constant, at least within the time frame of the split, then we can be relatively confident that, for short outages at least, we can predict the duration and hence the impact of an outage of the mirror.
While I'm not sure anyone will actually go for this — the impact of the data gathering process may be too sever to tolerate — I think it's worth pitching...
