LUDOC-531 mdt: Added more info on DoM EOF

Added details on the lfs setstripe -E option usage,
with a clear explanation of the end-of-file (EOF) handling.

Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
Change-Id: I8d828fd9e8124441afe6542e3a10e28085fe2991
Reviewed-on: https://review.whamcloud.com/c/doc/manual/+/56127
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>

diff --git a/DataOnMDT.xml b/DataOnMDT.xml
index de77c39..fb7d07d 100644 (file)
--- a/DataOnMDT.xml
+++ b/DataOnMDT.xml
@@ -31,6 +31,30 @@
       with a RAID0 layout. The OST components are not instantiated until
       a client writes or truncates the file beyond the size of the MDT
       component.</para>
+      <note>
+        <para>When specifying a DoM layout, it might be assumed that the
+          remaning layout will automatically go to the OSTs,
+          but this is not the case. As with regular PFL layouts, if an
+          <literal>EOF</literal> component is <emphasis>not</emphasis> present,
+          then writes beyond the end of the last existing component will fail
+          with error <literal>ENODATA</literal> (&quot;No data available&quot;).
+          For example, creating a DoM file with a component end at 1 MB will
+          not be writable beyond 1 MiB:</para>
+<screen>
+$ lfs setstripe -E 1M -L mdt /mnt/testfs/domdir
+$ dd if=/dev/zero of=/mnt/testfs/domdir/testfile bs=1M
+dd: error writing '/myth/tmp/pfl-mdt-only': No data available
+2+0 records in
+1+0 records out
+1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.00186441 s, 562 MB/s
+</screen>
+        <para>To allow the file to grow beyond 1 MB, add one or more regular
+          OST components with an <literal>EOF</literal> component at the end:
+        </para>
+<screen>
+lfs setstripe -E 1M -L mdt -E 1G -c1 -E eof -c4 /mnt/testfs/domdir
+</screen>
+      </note>
   </section>
   <section xml:id="usercommands">
       <title>