No, the algorithm is not purely random, it is weighted on QOS, space and a few other things.<div>When a stripe is chosen on one OSS, we add a penalty to the other OSTs on that OSS to prevent </div><div>IO bunching on one OSS. </div>
<div>cliffw</div><div> <br><br><div class="gmail_quote">On Thu, Mar 31, 2011 at 1:59 PM, Jeremy Filizetti <span dir="ltr"><<a href="mailto:jeremy.filizetti@gmail.com">jeremy.filizetti@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">I this a feature implemented after 1.8.5? In the past default striping without an offset resulted in sequential stripe allocation according to client device order for a striped file. Basically the order OSTs were mounted after the the last --writeconf is the order the targets are added to the client llog and allocated. <br>
<br>It's probably not a big deal for lots of clients but for a small number of clients doing large sequential IO or working over the WAN it is. So regardless of an A or B configuration a file with a stripe count of 3 could end up issuing IO to a single OSS instead of using round-robin between the socket/queue pair to each OSS.<br>
<font color="#888888">
<br>Jeremy</font><div><div></div><div class="h5"><br><br><div class="gmail_quote">On Thu, Mar 31, 2011 at 11:06 AM, Kevin Van Maren <span dir="ltr"><<a href="mailto:kevin.van.maren@oracle.com" target="_blank">kevin.van.maren@oracle.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex">
It used to be that multi-stripe files were created with sequential OST<br>
indexes. It also used to be that OST indexes were sequentially assigned<br>
to newly-created files.<br>
As Lustre now adds greater randomization, the strategy for assigning<br>
OSTs to OSS nodes (and storage hardware, which often limits the<br>
aggregate performance of multiple OSTs) is less important.<br>
<br>
While I have normally gone with "a", "b" can make it easier to remember<br>
where OSTs are located, and also keep a uniform convention if the<br>
storage system is later grown.<br>
<font color="#888888"><br>
Kevin<br>
</font><div><div></div><div><br>
<br>
Heckes, Frank wrote:<br>
> Hi all,<br>
><br>
> sorry if this question has been answered before.<br>
><br>
> What is the optimal 'strategy' assigning OSTs to OSS nodes:<br>
><br>
> -a- Assign OST via round-robin to the OSS<br>
> -b- Assign in consecutive order (as long as the backend storage provides<br>
> enought capacity for iops and bandwidth)<br>
> -c- Something 'in-between' the 'extremes' of -a- and -b-<br>
><br>
> E.g.:<br>
><br>
> -a- OSS_1 OSS_2 OST_3<br>
> |_ |_ |_<br>
> OST_1 OST_2 OST_3<br>
> OST_4 OST_5 OST_6<br>
> OST_7 OST_8 OST_9<br>
><br>
> -b- OSS_1 OSS_2 OST_3<br>
> |_ |_ |_<br>
> OST_1 OST_4 OST_7<br>
> OST_2 OST_5 OST_8<br>
> OST_3 OST_6 OST_9<br>
><br>
> I thought -a- would be best for task-local (each task write to own<br>
> file) and single file (all task write to single file) I/O since its like<br>
> a raid-0 approach used disk I/O (and SUN create our first FS this way).<br>
> Does someone made any systematic investigations which approach is best<br>
> or have some educated opinion?<br>
> Many thanks in advance.<br>
> BR<br>
><br>
> -Frank Heckes<br>
><br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>cliffw<div>Support Guy</div><div>WhamCloud, Inc. </div><div><a href="http://www.whamcloud.com" target="_blank">www.whamcloud.com</a></div><div><br></div><br>
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