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<div>Can anyone provide experiences with storage devices that use thin provisioning? I’ve been testing a few on them and I run into problems with the storage device incorrectly reporting the usage allocation after the files are deleted. I see this reference
in the GPFS FAQ, but I’m looking for some real-world experiences.</div>
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<div>Most flash devices use thin provisioning internally.</div>
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<div>Reference here:</div>
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<div><a href="https://www-01.ibm.com/support/knowledgecenter/api/content/nl/en-us/SSFKCN/com.ibm.cluster.gpfs.doc/gpfs_faqs/gpfsclustersfaq.html#thinprov" style="color: rgb(149, 79, 114);">https://www-01.ibm.com/support/knowledgecenter/api/content/nl/en-us/SSFKCN/com.ibm.cluster.gpfs.doc/gpfs_faqs/gpfsclustersfaq.html#thinprov</a></div>
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<div>Q4.12:</div>
<div>What are the considerations for using thinly provisioned or compressed volumes with GPFS?</div>
<div>A4.12:</div>
<div>While it is possible to use thinly provisioned (compression constitutes a form of thin provisioning) volumes with GPFS, there are some important configuration aspects that must be considered. Placing GPFS metadata on an NSD backed by a thinly provisioned
volume is dangerous and unsupported. If the real disk space backing a thinly provisioned virtual volume is exhausted, there is a possibility of a write to a previously allocated disk sector failing. If this volume hosts GPFS metadata, in certain scenarios
this could make a GPFS file system temporarily or even permanently unavailable. Placing GPFS data on a thinly provisioned volume is supported, but with certain limitations. Specifically, if the real disk space backing a thinly provisioned virtual volume is
exhausted, a failing data write could make the GPFS file system temporarily unavailable. <font color="#ff0000">Since at present GPFS does not communicate block deallocation events to the block device layer, freeing space on the file system layer does not free
up space on the block device layer. Thus it is possible for the efficiency of thin provisioning to degrade over time, as blocks as allocated and freed.</font></div>
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<font face="Helvetica">Bob Oesterlin<br>
Sr Storage Engineer, Nuance HPC Grid<br>
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