<font size=2 face="sans-serif">As primary developer of mmapplypolicy,
please allow me to comment:</font><br><br><font size=2 face="sans-serif">1) Fast access to metadata in system
pool is most important, as several have commented on. These days
SSD is the favorite, but you can still go with "spinning" media.<br>If you do go with disks, it's extremely important to spread your metadata
over independent disk "arms" -- so you can have many concurrent
seeks in progress at the same time. IOW, if there is a virtualization/mapping
layer, watchout that your logical disks don't get mapped to the same physical
disk.</font><br><br><font size=2 face="sans-serif">2) Crucial to use both -g and -N ::
-g /gpfs-not-necessarily-the-same-fs-as-Im-scanning/tempdir and -N
several-nodes-that-will-be-accessing-the-system-pool</font><br><br><font size=2 face="sans-serif">3a) If at all possible, encourage your
data and application designers to "pack" their directories with
lots of files. Keep in mind that, mmapplypolicy will read every
directory. The more directories, the more seeks, more time spent
waiting for IO. OTOH, in more typical Unix/Linux usage, we tend
to low average number of files per directory. </font><br><br><font size=2 face="sans-serif">3b) As admin, you may not be able to
change your data design to pack hundreds of files per directory, BUT you
can make sure you are running a sufficiently modern release of Spectrum
Scale that supports "data in inode" -- "Data in inode"
also means "directory entries in inode" -- which means practically
any small directory, up to a few hundred files, will fit in an an inode
-- which means mmapplypolicy can read small directories with one seek,
instead of two. </font><br><br><font size=2 face="sans-serif">(Someone will please remind us of the
release number that first supported "directories in inode".)<br></font><br><font size=2 face="sans-serif">4) Sorry, Fred, but the recommendation
to use RAID mirroring of metadata on SSD, is not necessarily, important
for metadata scanning. In fact it may work against you. If you use
GPFS replication of metadata - that can work for you -- since then GPFS
can direct read operations to either copy, preferring a locally attached
copy, depending on how storage is attached to node, etc, etc. Choice
of how to replicate metadata - either using GPFS replication or the RAID
controller - is probably best made based on reliability and recoverability
requirements.</font><br><br><font size=2 face="sans-serif">5) YMMV - We'd love to hear/see your
performance results for mmapplypolicy, especially if they're good. Even
if they're bad, come back here for more tuning tips!</font><br><br><font size=2 face="sans-serif">-- marc of Spectrum Scale (ne GPFS)</font><BR>