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RAID options supported by LVM
AIX LVM supports three RAID options.

RAID 0 Striping 
RAID 1 Mirroring 
RAID 10 or 0+1 Mirroring and striping 


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If possible, for easier system management and better performance, the default volume group, rootvg, should consist of only the physical volume on which the operating system is initially installed.

with Fast Write Cache, or disk arrays with write-cache) can provide for much better performance for log logical volumes (JFS log or database logs).


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Reorganizing logical volumes 
If you find that a volume was sufficiently fragmented to require reorganization, you can use the reorgvg command (or smitty reorgvg) to reorganize a logical volume and make it adhere to the stated policies.

This command will reorganize the placement of physical partitions within the volume group according to the logical volume characteristics. If logical volume names are specified with the command, highest priority is given to the first logical volume in the list. To use this command, the volume group must be varied on and have free partitions. The relocatable flag of each logical volume must be set to yes for the reorganization to take place, otherwise the logical volume is ignored.

By knowing the usage pattern of logical volumes, you can make better decisions governing the policies to set for each volume. Guidelines are:

Allocate hot LVs to different PVs. 
Spread hot LV across multiple PVs. 
Place hottest LVs in center of PVs, except for LVs that have Mirror Write Consistency Check turned on. 
Place coldest LVs on Edges of PVs (except when accessed sequentially). 
Make LV contiguous. 
Define LV to maximum size that you will need. 
Place frequently used logical volumes close together. 
Place sequential files on the edge. 


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Using raw disk I/O 
Some applications, such as databases, do not require a file system because they perform functions such as logging, keeping track of data, and caching. Performance of these applications is usually better when using raw I/O rather than using file I/O because it avoids the additional work of memory copies, logging, and inode locks.

When using raw I/O, applications should use the /dev/rlv* character special files. The /dev/lv* block special files should not be used, as they break large I/Os into multiple 4K I/Os. The /dev/rhdisk* and /dev/hdisk* raw disk interfaces should not be used because they degrade performance and can also cause data consistency problems.


