On Mon, Dec 15, 2008 at 7:57 PM, Thanos McAtos <[email protected]> wrote:
> Hello all. > > I'm doing a course project to evaluate recovery time of RAID-Z. > > One of my tests is to examine the impact of aging on recovery speed. > > I've used PostMark to stress the file-system but I didn't observe any > noticeable slowdown. > > Is there a better way to "age" a ZFS file-system? > > Does ZFS have aging issues at all? > > Thanx in advance. > <http://mail.opensolaris.org/mailman/listinfo/zfs-discuss> > Anton suggested some practical methods for conducting testing. But do follow proper testing procedure: Since you're doing this as part of a study course you may already know much of this, but I've just seen too many invalid, useless test to let this one pass. So firstly, understand that utilization metrics are not performance. At best they can be considered a symptom. However utilization metrics is important because it may provide hints at a) how to improve the system's performance, and b) errors in the thinking during the test design phase. Equally important: Know what your testing objectives are. Define important concepts, such as "recovery time" and "file system age". Document your test methodology, expected results, and make a list of scenarios, including a "base-line" for comparison, and a description of what will remain the same and what will be different between the test scenarios. For each test, record all utilization metrics so that you can evaluate these to understand what the bottleneck (bound resource) was in each scenario. Record the results for each test scenario. Include the recorded utilization data in an appendix. Make some conclusions. This is where definitions are important. For example saying that "file system age made [no] significant impact on raid-z recovery time" is completely meaningless unless you also defined "file system age" and "recovery time" The big issue is that everybody has got a case of "X performed better than Z, thus X is better than Z" where X and Z are simple products. You really have to accurately describe your test scenarios, especially in terms of what are different and what are the same between them. Try to be as complete as possible. Include the scripts and their parameters as you used them to generate load, if possible (Not possible when you let users generate real load) So some items to list in your scenarios: o System configuration details. o OS version, patches o Software versions (patch revisions, etc) o Configuration details (at least anything which is non-default. In many case you may want to specifically stress some default values) o The exact test procedure, parameters, etc. So, while talking about Raid-Z recovery time, particularly in terms of the File System "age", I imagine some kind of comparison of recovery times. I am sure you will design a series of increasingly "aged" storage pools, and for each perform a number of "recovery test" for which you will record the run time. What would be your baseline? What do you want to keep constant between the tests? Nr of files? File system usage level? Nr of disks in the pool? I am assuming that not changing the system configuration and patch level between the test scenarios are obvious. I am also assuming that system load will be idle for all tests? In terms of evaluating the results: Do you expect the file system age to actually impact on the recovery time? If so, is this based on how file system age impacts on recovery time for other raid technologies? If your test results will be published I'd love to take a look at it. Good luck -- Any sufficiently advanced technology is indistinguishable from magic. Arthur C. Clarke My blog: http://initialprogramload.blogspot.com
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