A logical extent is a group of data blocks that are logically aligned and logically contiguous. When you enable logical extents, Data ONTAP processes write operations by creating groups of logically contiguous data blocks that are physically close to each other on the disk. Extents optimize sequential data block layout and improve the amount of time required for applications to perform sequential read operations, such as database scans.
In Microsoft Exchange environments, you use the Exchange eseutil tool to perform database scans for validation purposes. Exchange database scans access data by mostly using a sequential read pattern. By enabling logical extents, you improve Exchange sequential read performance and database validation time.
You enable logical extents for volumes that contain Microsoft Exchange data only. The decision to use logical extents involves a trade-off between improved database validation performance and runtime performance. You use logical extents when you want to improve validation performance. If runtime performance is higher priority, you might not want to use extents.
You can enable logical extents on a traditional or FlexVol volume. To enable logical extents, enter the following command:
vol options vol-name extent [on | off]
on enables logical extents for the volume.
off disables logical extents for the volume. By default, logical extents are disabled.
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Part No. 210-01094_B0
File: c10perf3.htm
Last updated: 08-Dec-2005 13:25:38