Installation guide

Appendix A. The Device Mapper
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The following example shows a pure failover target definition for the same multipath device. In this
target there are four path groups, with only one open path per path group so that the multipathed
device will use only one path at a time.
0 71014400 multipath 0 0 4 1 round-robin 0 1 1 66:112 1000 \
round-robin 0 1 1 67:176 1000 round-robin 0 1 1 68:240 1000 \
round-robin 0 1 1 65:48 1000
The following example shows a full spread (multibus) target definition for the same multipathed device.
In this target there is only one path group, which includes all of the paths. In this setup, multipath
spreads the load evenly out to all of the paths.
0 71014400 multipath 0 0 1 1 round-robin 0 4 1 66:112 1000 \
67:176 1000 68:240 1000 65:48 1000
For further information about multipathing, see the Using Device Mapper Multipath document.
A.1.8. The crypt Mapping Target
The crypt target encrypts the data passing through the specified device. It uses the kernel Crypto
API.
The format for the crypt target is as follows:
start length crypt cipher key IV-offset device offset
start
starting block in virtual device
length
length of this segment
cipher
Cipher consists of cipher[-chainmode]-ivmode[:iv options].
cipher
Ciphers available are listed in /proc/crypto (for example, aes).
chainmode
Always use cbc. Do not use ebc; it does not use an initial vector (IV).
ivmode[:iv options]
IV is an initial vector used to vary the encryption. The IV mode is plain or essiv:hash. An
ivmode of -plain uses the sector number (plus IV offset) as the IV. An ivmode of -essiv
is an enhancement avoiding a watermark weakness.
key
Encryption key, supplied in hex
IV-offset
Initial Vector (IV) offset