In addition to the explicit limits on number of volumes (64), number of partitions per drive (32), and drives per stripe (16), the size of the driver memory pool and the mix of volume types limits the number of volumes which can be created by Conley's RAID software applications. Version 1.5 of Conley's RAID software enforces the driver memory limits. Earlier [unreleased] versions did not, which allowed too many volumes to be created, which used up driver memory and led to crashes. Because the released version of the software enforces the limits, driver memory should not be an issue in real-world use of the software, but this information is presented here as an FYI.
Driver memory currently defaults to 256K (it can be changed by editing a resource in the application). Of this 256K, 80K is reserved for driver operation and 32K for mirror rebuilds. The remaining 144K can be used to support volumes. Each new or exisitng volume requires the following amounts of driver memory:
HFS Volume: 1360 bytes
Mirrored Volume: 2656 bytes
Striped Volume: 6304 + (n * 1152) bytes, where n is the number of drives in the stripe MINUS 2.
With the default driver memory of 256K, the following table indicates the maximum number of volumes of different types which can be created, assuming only one type of volume is present:
Normal | Mirror | Stripes, with number of drives |
Vols | Vols | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 |11 | 12 | 13 |14 |15 |16 |
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108 | 55 | 23| 19| 17| 15| 13| 12| 11| 10| 9 | 8 | 8 | 7 | 7 | 6 | 6 |If 512K is specified, the following table holds:
Normal | Mirror | Stripes, with number of drives |
Vols | Vols | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 |11 | 12 | 13 |14 |15 |16 |
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325 | 166 | 70| 59| 51| 45| 40| 36| 33| 30| 28| 26| 24 | 23 | 21| 20| 19|If a mix of volume types is present, the actual limits will vary within the ranges shown in the tables.
This article was published in the 25 June 1997 "Information Alley".