HADB Storage Capacity

The HADB provides near-linear scaling with the addition of more nodes until the network capacity is exceeded. Each node must be configured with storage devices on a dedicated disk or disks. All nodes must have equal space allocated on the storage devices. Make sure that the storage devices are allocated on local disks.

Suppose the expected size session data is x MB. HADB replicates data on mirror nodes, and therefore requires 2x MB of storage. Further, HADB uses indexes to enable fast access to data. The two nodes will require an additional 2x MB for indexes, for a total required storage capacity of 4x. Therefore, HADB’s expected storage capacity requirement is four times the expected data volume.

To account for future expansion without loss of data from HADB, you must provide additional storage capacity for online upgrades because you might want to refragment the data after adding new nodes. In this case, a similar amount (4x) of additional space on the data devices is required. Thus, the expected storage capacity is eight times the expected data volume.

Additionally, HADB uses disk space as follows:

• Space for temporary storage of log buffer. This space is four times the log buffer size. The log buffer keeps track of operations related to data. The default value of the log buffer size is 48 MB.

• Space for internal administration purpose. This space is one percent of the storage device size.

The following table summarizes the HADB storage space requirements for a session data of x MB.

Table 2–3 HADB Storage Space Requirement for Session Size of X MB

Condition	HADB Storage Space Required
Addition or removal of HADB nodes while online is not required.	4x MB + (4*log buffer size) + 1% of device size
Addition or removal of HADB nodes while online is required.	8x MB + (4*log buffer size) + 1% of device size

If the HADB runs out of device space, it will not accept client requests to insert or update data. However, it will accept delete operations. If the HADB runs out of device space, it returns error codes 4593 or 4592 and writes corresponding error messages to the history files. For more information on these messages, seeChapter 14, HADB Error Messages, in Sun Java System Application Server 9.1 Error Message Reference.