7.7.4.4 CREATE FLASHCACHE

Purpose

The CREATE FLASHCACHE command creates Exadata Smart Flash Cache on a cell for I/O requests.

Syntax

CREATE FLASHCACHE { ALL [size=fc_size] | CELLDISK="cdisk1 [,cdisk2] ..." [, size=fc_size] }

Usage Notes

Cell disks defined on Exadata Smart Flash Cache cannot be exported.

The ALL argument creates Exadata Smart Flash Cache on all flash cell disks. If the ALL argument is not specified, then the CELLDISK argument must be specified.

Using the CELLDISK argument, you can specify a list of flash cell disks to be used for flash cache. The names of the flash cell disks are comma-delimited. The FLASHDISK argument is not required.

The size argument specifies the total space used for flash cache. Similar to space in grid disks and flash logs, flash cache space is allocated in 16 MB units, referred to as allocation units. If the size attribute is specified when creating a flash cache, then the size allocated is the size of the largest multiple of allocation units less than or equal to the specified size. For example, if 300M is specified for the size attribute, then 288 MB (16x18) is allocated because 288 is the largest multiple of 16 that is less than or equal to 300.

A minimum of 1 allocation unit is always allocated, so the minimum size for a flash cache is 16 MB. Any size value less than 16 MB is rounded up to 16 MB.

Before specifying the size attribute, ensure that you have first determined the available free space on each target flash cell disk with the LIST FLASHCACHE command. For example, LIST FLASHCACHE ATTRIBUTES freespace. If the size attribute is not specified, then the maximum size is allocated.

If the size attribute is not specified, then all available space on each cell disk in the list is used for Exadata Smart Flash Cache.

By default, 5 percent of space on Extreme Flash storage servers is used for write-back flash cache.

Examples

Example 7-82 Creating Exadata Smart Flash Cache

This example shows how to create Exadata Smart Flash Cache on a cell.

CellCLI> CREATE FLASHCACHE ALL

CellCLI> CREATE FLASHCACHE ALL SIZE=250g

CellCLI> CREATE FLASHCACHE CELLDISK='fd_01,fd_02,fd_03,fd_04'

CellCLI> CREATE FLASHCACHE CELLDISK='fd_01_mycell,fd_02_mycell', size = 64G