content_image/1012519.jpg
GLYPH<SM590000> Warning threshold:  Whether a warning message should be sent, and at what percentage of filled virtual capacity. Defaults to Enabled , with a warning threshold set at 80%. 

GLYPH<SM590000> Thin-Provisioned Grain Size:  Allows you to define the grain size for the thin-provisioned volume. Defaults to 256 KiB. 

Important:  If you do not use the autoexpand  feature, the volume goes off line if it receives a write request after all real capacity is allocated. 

The default grain size is 256 KiB. The optimum choice of grain size is dependent upon volume-use type. Consider these points: 

GLYPH<SM590000> If you are not  going to use the thin-provisioned volume as a FlashCopy source or target volume, use 256 KiB to maximize performance. 

GLYPH<SM590000> If you are  going to use the thin-provisioned volume as a FlashCopy source or target volume, specify the same grain size for the volume and for the FlashCopy function. 

GLYPH<SM590000> If you plan to use EasyTier with thin-provisioned volumes, then review the IBM Support article Performance Problem When Using EasyTier With Thin Provisioned Volumes  at: 

## Compressed pane 

http://www.ibm.com/support/docview.wss?uid=ssg1S1003982 

If you choose to create a compressed volume, a Compressed pane is displayed, as shown in Figure 7-21. 

<img src='content_image/1012519.jpg'>

This pane gives the following options: 

GLYPH<SM590000> Real capacity:  Real capacity of the volume, specified either as percentage of the virtual capacity, or in bytes. 

GLYPH<SM590000> Automatically expand:  Whether to automatically expand the real capacity of the volume if needed. Defaults to Enabled . 

GLYPH<SM590000> Warning threshold:  Whether a warning message should be sent, and at what percentage of filled virtual capacity. Defaults to Enabled , with a warning threshold set at 80%. 

You cannot specify grain size for a compressed volume. 

Note:  Before you create the first compressed volume copy on a system, consider the compression guidelines in Chapter 10, “Advanced features for storage efficiency” on page 427. 

