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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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norewind_close_disabled(5)					File Formats Manual					norewind_close_disabled(5)

NAME
norewind_close_disabled - determine whether access to tape device special files without the no-rewind-on-close option is allowed VALUES
Default Allowed values DESCRIPTION
Note: this tunable was named in releases prior to HP-UX 11i v3. This tunable notifies the tape driver whether it should allow access to device special files without the no-rewind-on-close option. When this tunable is on, the tape driver will fail any open on a tape device special file that does not have the no-rewind-on-close option (that is, or with a status of The tunable allows the safe sharing of tape devices in SAN tape backup solution configurations. The disabling of device special files without no-rewind-on-close in a SAN tape backup solution configuration prevents the accidental sending of a rewind command on close from HP-UX systems via standard tape commands like which would corrupt a backup in process. Who Is Expected to Change This Tunable? Anyone. Restrictions on Changing Changes to this tunable take effect immediately. When Should the Tunable Be Turned On? This tunable should be turned on if the system is going to be used in a SAN tape backup solution configuration. What Are the Side Effects of Turning the Tunable On? The tape driver will fail any open to a tape device special file that does not have the no-rewind-on-close option with a status of This behavior prevents the usage of any tape device special file without the no-rewind-on-close option. When Should the Tunable Be Turned Off? This tunable should be turned off if the system is not part of a SAN tape backup solution configuration or the system utilizes will not function unless it has access to device special files without the no-rewind-on-close option. What Are the Side Effects of Turning the Tunable Off? A rewind may be issued accidentally from this system on close, possibly corrupting a backup being issued from another system on the SAN. What Other Tunables Should Be Changed at the Same Time? None. EXAMPLES
Query the current value of the tunable: Set the value of the tunable to To save the value of the tunable across reboots: WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX. Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun- able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see at AUTHOR
was developed by Hewlett-Packard. SEE ALSO
scsi_tape(7), scsimgr_estape(7). Tunable Kernel Parameters norewind_close_disabled(5)
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