Improving performance with low DRIVE STARTUP THRESHOLD value

Using a low DRIVE STARTUP THRESHOLD value can allow objects to write concurrently during the storage management cycle, resulting in improved performance and reduced cycle time for the storage group. If more than one drive is used for writing, then the writing of an object to a volume is interspersed with the writing of other objects to their respective volumes. Objects for only one storage group reside on the two optical volumes on an optical disk. Spreading data across volumes makes those volumes unavailable for other storage groups.

You can choose different DRIVE STARTUP THRESHOLD values for different storage groups, allowing you to choose independently between drive write concurrency and the volume-fill characteristic for each of the groups.

The determination of the DRIVE STARTUP THRESHOLD is the same for both Object and Object Backup storage groups.

Recommendation: Make certain that you have enough usable optical disks per storage group (scratch or already assigned to the storage group) to be used simultaneously for the write requests to the storage group once the DRIVE STARTUP THRESHOLD is crossed. OAM does not issue any message to request additional space for a storage group when the DRIVE STARTUP THRESHOLD is crossed and additional space for the storage group is not available. If the DRIVE STARTUP THRESHOLD is crossed, and there are no usable optical disks available, it is as if the threshold were never crossed; OAM continues to perform the write requests on the existing busy disks. Performance is slower than it would have been if additional space had been available when the threshold was crossed.

Table 1 contains information to help you select a value for DRIVE STARTUP THRESHOLD, based on average object size and the number of drives on which concurrent activity is permitted. If your average object size is slightly larger or smaller than the size shown in the table, adjust the DRIVE STARTUP THRESHOLD value accordingly.

Table 1. Recommended values for DRIVE STARTUP THRESHOLD
Average object size in bytes	Activity on one drive only	Activity on two drives	Activity on three drives
3 000	>= 4680	2340–4679	1560–2339
4 000	>= 3600	1800–3599	1200–1799
5 000	>= 2880	1440–2879	960–1439
8 000	>= 1800	900–1799	600–899
16 000	>= 864	432–863	288–431
32 000	>= 432	216–431	144–215
40 000	>= 360	180–359	120–179
64 000	>= 216	108–215	72–107
100 000	>= 144	72–143	48–71
128 000	>= 108	54–107	36–53
256 000	>= 48	24–47	16–23
512 000	>= 24	12–23	8–11
1␠000␠000	>= 9	5–8	3–4
2␠000␠000	>= 5	3–4	2