Note – The data block size must be configured before any logical volumes are created on the units. Remember, this block size is used for every logical volume created on the unit. Therefore it is important to have similar application data configured per unit.
Data block size is universal throughout a partner group. Therefore, you cannot change it after you have created a volume. To change the data block size, you must first delete the volume(s), change the data block size, and then create new volume(s).
Caution – Unless you back up and restore the data on these volumes, it will be lost.
Enabling Mirrored Cache
By enabling mirrored cache, you can safeguard cached data if a controller fails.
Note – Mirrored cache is possible only in a redundant enterprise configuration.
Configuring Cache Allocation
Cache is allocated based on the read/write mix and it is dynamically adjusted by the controller firmware, based on the I/O profile of the application. If the application profile is configured for a 100% read environment, then 100% of the cache is used for reads. If the application profile has a high number of writes, then the upper limit for writes is set to 80%.
Logical Volumes
Also called a logical unit number (LUN), a logical volume is one or more disk drives that are grouped together to form a single unit. Each logical volume is represented to the host as a logical unit number. Using the format utility on the application host, you can view the logical volumes presented by the array. You can use this disk space as you would any physical disk, for example, to perform the following operations:
■Install a file system
■Use the device as a raw device (without any file system structure)
■Partition the device