2009/4/8 Alexander Zarochentsev <span dir="ltr"><<a href="mailto:Alexander.Zarochentsev@sun.com">Alexander.Zarochentsev@sun.com</a>></span><br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hello Nikita!<br>
<div><div></div><div class="h5"><br>
On 7 April 2009 11:50:29 Nikita Danilov wrote:<br>
> 2009/4/7 Alex Zhuravlev <<a href="mailto:bzzz@sun.com">bzzz@sun.com</a>><br>
><br>
> > >>>>> Andreas Dilger (AD) writes:<br>
><br>
> Hello,<br>
></div></div></blockquote><div></div><div>[...]<br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div class="h5">> $ echo > a/b/c/d/file # truncate secret data<br>
> $ chmod 777 a # relax permissions<br>
><br>
> Note that here an ordering between data and meta-data updates on<br>
> _different_ objects is important.<br>
<br>
</div></div>If we only guarantee no reordering in MD updates, Lustre behavior would<br>
be like ext3 without data journalling? I think it is not terrible.</blockquote><div><br>It's not terrible, but it is non-intuitive, in my opinion. More enlightened file systems, like ZFS, reiser4, and NTFS provide stronger consistency guarantees, ignoring the petty distinctions between data and meta-data. :-)<br>
<br>But even limiting consistency to meta-data leaves some issues opened. For example, think about an md proxy server acting as a WBC client for a higher tier server. To be efficient such proxy might need to cache very large amount of meta-data, and it most likely cannot afford to keep a log of all operations. In this situation, when a lock on a top-level directory gets a blocking AST, proxy would have --to guarantee ordering of visible meta-data updates-- to write back all cached dirty meta-data under this directory before the lock can be cancelled, which might result in unacceptable latency.<br>
<br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">><br>
> > thanks, Alex<br>
><br>
> Nikita.<br>
<br>
</div><div><div></div><div class="h5">--<br>
Alexander "Zam" Zarochentsev</div></div></blockquote><div><br>Nikita.<br></div></div><br>