Kernel parameters

6.18 LPAR mode z/VM guest KVM guest

If the base module of the DASD device driver has been compiled into the kernel, you configure the device driver by adding parameters to the kernel parameter line.

Figure 1. DASD kernel parameter syntax

where:

autodetect: causes the DASD device driver to allocate device names and the corresponding minor numbers to all DASD devices and set them online during the boot process.
The device names are assigned in order of ascending subchannel numbers. Auto-detection can yield confusing results if you change your I/O configuration and reboot, or if your Linux® instance runs as a z/VM® guest because the devices might appear with different names and minor numbers after rebooting.
probeonly: causes the DASD device driver to reject any open syscall with EPERM.
autodetect,probeonly: causes the DASD device driver to assign device names and minor numbers as for auto-detect. All devices regardless of whether they are accessible as DASD return EPERM to any open requests.
nopav: suppresses parallel access volume (PAV and HyperPAV) enablement for Linux instances that run in LPAR mode. The nopav keyword has no effect for Linux on z/VM.
nofcx: suppresses accessing the storage server with the I/O subsystem in transport mode (also known as High Performance FICON®).
<device_bus_id>: specifies a single DASD.
<from_device_bus_id>-<to_device_bus_id>: specifies the first and last DASD in a range. All DASD devices with bus IDs in the range are selected. The device bus-IDs <from_device_bus_id> and <to_device_bus_id> need not correspond to actual DASD.
ipldev: for IPL from a DASD, specifies the IPL device. If the IPL device is not a DASD, this parameter is ignored.
(ro): accesses the specified device or device range in read-only mode.
(diag): forces the device driver to access the device (range) with the DIAG access method.
(erplog): enables enhanced error recovery processing (ERP) related logging through syslogd. If erplog is specified for a range of devices, the logging is switched on during device initialization.
(failfast): immediately returns failed for an I/O operation when the last path to a DASD is lost.
Attention: Enable immediate failure of I/O requests only in setups where a failed I/O request can be recovered outside the scope of a single DASD.

If you supply a DASD kernel parameter with device specifications dasd=<device-list1>,<device-list2> ..., the device names and minor numbers are assigned in the order in which the devices are specified. The names and corresponding minor numbers are always assigned, even if the device is not present, or not accessible.

If you use autodetect in addition to explicit device specifications, device names are assigned to the specified devices first and device-specific parameters, like ro, are observed. The remaining devices are handled as described for autodetect.

Example

The following kernel parameter specifies a range of DASD devices and two individual DASD devices.

dasd=0.0.7000-0.0.7002,0.0.7005(ro),0.0.7006

Table 1 shows the resulting allocation of device names and minor numbers:

Table 1. Example mapping of device names and minor numbers to devices
Minor	Name	To access
0	dasda	device 0.0.7000 as a whole
1	dasda1	the first partition on 0.0.7000
2	dasda2	the second partition on 0.0.7000
3	dasda3	the third partition on 0.0.7000
4	dasdb	device 0.0.7001 as a whole
5	dasdb1	the first partition on 0.0.7001
6	dasdb2	the second partition on 0.0.7001
7	dasdb3	the third partition on 0.0.7001
8	dasdc	device 0.0.7002 as a whole
9	dasdc1	the first partition on 0.0.7002
10	dasdc2	the second partition on 0.0.7002
11	dasdc3	the third partition on 0.0.7002
12	dasdd	device 0.0.7005 as a whole
13	dasdd1	the first partition on 0.0.7005 (read-only)
14	dasdd2	the second partition on 0.0.7005 (read-only)
15	dasdd3	the third partition on 0.0.7005 (read-only)
16	dasde	device 0.0.7006 as a whole
17	dasde1	the first partition on 0.0.7006
18	dasde2	the second partition on 0.0.7006
19	dasde3	the third partition on 0.0.7006