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Full Discussion: IBM SAN TO SAN Mirroring
Operating Systems AIX IBM SAN TO SAN Mirroring Post 302717149 by DGPickett on Wednesday 17th of October 2012 03:33:37 PM
Old 10-17-2012
Well, I am sure most SAN can be configured for mirroring, which is raid-2 or something like that. To achieve the most bang for your buck, you want the mirrors to be as far apart as possible, so something between the application host and short of the storage box needs to know where there are 2 so it can sidestep the dead side as well as splitting the query load and duplicating the churn. The farther upstream it is done, the greater the reliability, but too close can load the app server and communications, unless fiber has multicast write and anycast read. There may be several layers vying to mirror your storage, so pick wisely.

Mirroring got overshadowed a bit by raid, but has always had a query bandwidth advantage, with two devices handling query. Within the devices, there can be as much striping as in raid, so that is no different. When writing, there is no parity calculation and additional write time, just two immediate simultaneous writes. With raid in sequential striping mode, you write data to 1,2,3,4 and parity to 5, then data to 5,1,2,3 and parity to 4, and so on, so while reading is 5x spindle speed, writing is 4x. A mirrored pair trades space for bandwidth. Disk is cheap, and bandwidth is golden. Finally, it seems some raid systems seem to only get defects detected by staff when 2 adjacent devices fail, so often raid5 is either also mirrored or great downtime, data loss and partial restore pain is experienced.
 

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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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