[DRBD-user] What is term "active set" means and what size to choose?

Igor Yu. Zhbanov bsg at uniyar.ac.ru
Tue Jun 21 17:26:02 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


In sample drbd.conf there is an option al-extents:

    # Configures the size of the active set. Each extent is 4M,
    # 257 Extents ~> 1GB active set size. In case your syncer
    # runs @ 10MB/sec, all resync after a primary's crash will last
    # 1GB / ( 10MB/sec ) ~ 102 seconds ~ One Minute and 42 Seconds.
    # BTW, the hash algorithm works best if the number of al-extents
    # is prime. (To test the worst case performace use a power of 2)
    al-extents 257;

What is "active set"? What will be if I will set small size for it?

I have 1,2 TB RAID array as low-level storage for DRBD. How to determine
optimal value for al-extents parameter? Is it depends on disk size or number
of files or activity on that disk?


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