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Full Discussion: SAN vs. Local disk.
Top Forums UNIX for Beginners Questions & Answers SAN vs. Local disk. Post 303031269 by rbatte1 on Monday 25th of February 2019 06:26:43 AM
Old 02-25-2019
It all comes down to the homonyms cash & cache.

How much is you budget for cache? That's the key really. SSD is slightly slower than cache.

For write operations, you would have to balance off the time to commit the update to real disk (even if it is SSD) between the two. if you pass the update to a SAN, it will respond very quickly to say that you have written it, but it will actually write the data in its own time. The update is cached for write but you can continue. There will be cache batteries for power loss before it's really written. For local disk, it depends. Does the RAID controller have a good cache allocation and would therefore behave in the same way? If not, you (the operating system) must ensure that the write is complete before you proceed (costing CPU Sys time I think) and that can confusingly make local IO slower.

You have, of course, stated that this is a read intensive server so your other thing to consider is cache/RAM in the server. The server will fill up with the data you read in normally anyway, but if you wish, you could pre-read the data to give it a head-start. Beware that you need to have lots of memory for this else you will just drop it again. You can just do a find for the files of data you want and cat them to /dev/null so that they get read. Is 512Gb sufficient for your data? You don't say how much you have.



I hoe that my thoughts help,
Robin
 

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LEARN ABOUT CENTOS

mkqdisk

mkqdisk(8)						      Quorum Disk Management							mkqdisk(8)

NAME

       mkqdisk - Cluster Quorum Disk Utility

WARNING

       Use of this command can cause the cluster to malfunction.

SYNOPSIS

       mkqdisk [-?|-h] | [-L] | [-f label] [-c device  -l label] [-d [-d ...]]

DESCRIPTION

       The mkqdisk command is used to create a new quorum disk or display existing quorum disks accessible from a given cluster node.

OPTIONS

       -c device -l label
	      Initialize  a new cluster quorum disk.  This will destroy all data on the given device.  If a cluster is currently using that device
	      as a quorum disk, the entire cluster will malfunction.  Do not run this on an active cluster  when  qdiskd  is  running.	 Only  one
	      device  on  the  SAN should ever have the given label; using multiple different devices is currently not supported (it is expected a
	      RAID array is used for quorum disk redundancy).  The label can be any textual string up to 127 characters - and is therefore  enough
	      space to hold a UUID created with uuidgen(1).

       -f label
	      Find the cluster quorum disk with the given label and display information about it.

       -L     Display information on all accessible cluster quorum disks.

       -d     Increase debugging level.  Specify multiple times for more information.  Currently, specifying more than twice has no effect.

SEE ALSO

       qdisk(5), qdiskd(8), uuidgen(1)

								     July 2006								mkqdisk(8)
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