Creating a cache area


Creating a cache area
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SmartIO introduces the concept of a cache area. The cache area is the storage space that SmartIO uses to store the cached data and the metadata about the cached data. You create a cache area to use for I/O caching. Usually, you use SSD devices or other fast devices for the cache area. A cache area can be used for VxFS caching or VxVM caching. You can create only one cache area of each type on each system.

To create a cache area on a device, specify the device name (disk access name) or the name of a disk group and volume on the device.

By default, a cache area has an association type of auto. All of the data objects of the same type (VxVM or VxFS) are implicitly associated with the auto cache area. If the association type is noauto, you must explicitly associate the data objects to the cache area.

In a cluster, each node has a separate, local cache area.

To create a VxVM cache area

Create the VxVM cache area on the SSD device, using one of the following commands:
- Specify one or more devices using the disk access name (daname) of the device. The device should be initialized for VxVM use and have the cdsdisk format.
```
# sfcache create -t VxVM [size] daname[...] \
[cacheline_size=cacheline_size] [--auto|--noauto] [--nostripe|ncols=N] \
[cachearea_name]
```
  Where:
  
  daname specifies the disk access name of the device on which to create the cache area.
  
  cachearea_name specifies a customized name for the cache area. If unspecified, the SmartIO feature automatically generates a name for the cache area.
  
  size specifies the size for the cache area. By default, the cache area uses all of the available space on the device.
  
  --noauto|--auto specifies the type of cache area. The default is --auto.
  
  --nostripe|ncols=n specifies the layout options for the cache area. By default, the cache area is created over a striped volume if two or more disks are specified. Use the ncols=n option to specify the number of columns for the striped volume. Use the --nostripe option to create the cache area on a concatenated volume over the specified disks.
  
  cacheline_size specifies the unit that SmartIO uses for caching. When the application I/O accesses the data, the SmartIO moves the data to the cache according to the cacheline size. Generally, you do not need to change the cacheline_size.
  
  For example:
```
# sfcache create -t VxVM ssd0_0
```
  If you specify more than one disk, the cache area is striped across the specified disks by default. For example:
```
# sfcache create -t VxVM ssd0_0 ssd0_1
```
- Alternatively, you can specify the name of a disk group and a volume to use for the cache area. In this case, you cannot specify a size: the cache area uses the entire volume.
```
# sfcache create -t VxVM  [cacheline_size=cacheline_size] \
 [--noauto|--auto] dg/vol
```
  Where:
  
  dg/vol specifies the disk group name and volume name that you want to use for the cache area. SmartIO uses this name for the cache area.
  
  --noauto|--auto specifies the association type of the cache area. The default is --auto.
  
  For example:
```
# sfcache create -t VxVM --auto ssd_dg/ssd_vol
```

To create a VxFS cache area

Create the VxFS cache area on the SSD device, using one of the following commands.
- Specify one or more devices using the disk access name (daname) of the device. The device should be initialized for VxVM use and have the cdsdisk format.
```
# sfcache create [-t VxFS] [size] daname[...] [--auto|--noauto] \
 [--nostripe|ncols=N] [cachearea_name]
```
  Where:
  
  daname specifies the disk access name of the device on which to create the cache area.
  
  cachearea_name specifies a customized name for the cache area. If unspecified, the SmartIO feature automatically generates a name for the cache area.
  
  size specifies the size for the cache area. By default, the cache area uses all of the available space on the device.
  
  --noauto|--auto specifies the type of cache area. The default is --auto.
  
  For example:
```
# sfcache create ssd0_0
```
  --nostripe|ncols=n specifies the layout options for the cache area. By default, the cache area is created over a striped volume if two or more disks are specified. Use the ncols=n option to specify the number of columns for the striped volume. Use the --nostripe option to create the cache area on a concatenated volume over the specified disks.
- Alternatively, you can specify the name of a disk group and a volume to use for the cache area. In this case, you cannot specify a size: the cache area uses the entire volume.
```
# sfcache create [-t VxFS] [--noauto|--auto] dg/vol
```
  Where:
  
  dg/vol specifies the disk group name and volume name that you want to use for the cache area. SmartIO uses this name for the cache area.
  
  --noauto|--auto specifies the type of cache area. The default is --auto.
  
  For example:
```
# sfcache create --auto ssd_dg/ssd_vol
```