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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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dsbitmap(1M)						  System Administration Commands					      dsbitmap(1M)

NAME
dsbitmap - size Availability Suite bitmap volumes SYNOPSIS
dsbitmap -h dsbitmap -p data_volume [bitmap_volume] dsbitmap -r data_volume [bitmap_volume] DESCRIPTION
The dsbitmap command calculates the size of the Availability Suite bitmap volume required for use with the specified data volume. OPTIONS
The following options are supported: -h Prints the usage message for the dsbitmap command -p data_volume [bitmap_volume] For the given data_volume, dsbitmap calculates and display the required size for the associated Availability Suite Point in Time bitmap volume. The bitmap volume sizes for all possible Availability Suite Point in Time set configurations are displayed. These configura- tions include Independent shadow, Full size dependent shadow, and Compact dependent shadow. If the optional bitmap_volume argument is supplied, dsbitmap determines if this volume is large enough to be used as the bitmap volume for data_volume. -r data_volume [bitmap_volume] For the given data_volume, dsbitmap calculates and displays the required size for the associated Availability Suite Remote Mirror bit- map volume. The bitmap volume sizes for all possible Availability Suite Remote Mirror set configurations are displayed. These configu- rations include Sync replication, Async replication with memory queue, disk queue and 32 bit refcount. If the optional bitmap_volume argument is supplied, dsbitmap determines if this volume is large enough to be used as the bitmap volume for data_volume. USAGE
dsbitmap is typically used by the system administrator during the initial stages of configuring Sun StorageTek Availability Suite software in order to determine the required bitmap volume sizes, and then to check if the bitmap volumes that have been created are suitable. EXIT STATUS
The following exit values are returned: 0 Successful completion. If the name of a bitmap volume was specified, that volume is sufficiently large for all potential uses. 1 An error occurred. 2 An invalid option was supplied on the command line. 3 The specified bitmap volume is not large enough to be used as an Availability Suite Remote Mirror bitmap for an asynchronous set with a disk queue, but is large enough to be used for all other Remote Mirror set configurations. 4 The specified bitmap volume is not large enough to be used as an Availability Suite Remote Mirror bitmap for any Remote Mirror set configuration. 5 The specified bitmap volume is not large enough to be used as an Availability Suite Remote Mirror bitmap for any Remote Mirror set configuration. 6 The specified bitmap volume is not large enough to be used as an Availability Suite Point in Time bitmap for a compact depen- dent shadow, but is large enough to be used for all other Point in Time set configurations. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscmr, SUNWscmu | +-----------------------------+-----------------------------+ |Interface Stability |Evolving | +-----------------------------+-----------------------------+ SEE ALSO
iiadm(1M), sndradm(1M), attributes(5) SunOS 5.11 2 Oct 2007 dsbitmap(1M)
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