<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, May 19, 2015 at 4:26 PM, Jeff Darcy <span dir="ltr"><<a href="mailto:jdarcy@redhat.com" target="_blank">jdarcy@redhat.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">> No, my suggestion was aimed at not having parallel writes. In this case quota<br>
> won't even fail the writes with EDQUOT because of reasons explained above.<br>
> Yes, we need to disable flush-behind along with this so that errors are<br>
> delivered to application.<br>
<br>
</span>Would conv=sync help here? That should prevent any kind of write parallelism.<br></blockquote><div><br></div><div>An strace of dd shows that<br><br></div><div>* fdatasync is issued only once at the end of all writes when conv=fdatasync<br></div><div>* for some strange reason no fsync or fdatasync is issued at all when conv=sync<br><br></div><div>So, using conv=fdatasync in the test cannot prevent write-parallelism induced by write-behind. Parallelism would've been prevented only if dd had issued fdatasync after each write or opened the file with O_SYNC.<br></div><div><br></div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
If it doesn't, I'd say that's a true test failure somewhere in our stack. A<br>
similar possibility would be to invoke dd multiple times with oflag=append.<br></blockquote><div><br></div><div>Yes, appending writes curb parallelism (at least in glusterfs, but not sure how nfs client behaves) and hence can be used as an alternative solution.<br><br></div><div>On a slightly unrelated note flush-behind is immaterial in this test since fdatasync is anyways acting as a barrier.<br><br></div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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