ramdisk - RAM disk device driver
The ramdisk driver supports numerous ramdisk devices that
are created by the system during the boot process (see
boot(1M)) or during normal system operation (see
ramdiskadm(1M) for more information).
DEVICE SPECIAL FILES
Each ramdisk can be accessed either as a block device or as
a raw device. When accessed as a block device, the normal
buffering mechanism is used when reading from and
writing to the device, without regard to physical disk
records. Accessing the ramdisk as a raw device enables
direct transmission between the disk and the read or write
buffer. A single read or write call usually results in a
single I/O operation, meaning that raw I/O is more effi-
cient when many bytes are transmitted. You can find block
files names in /dev/ramdisk. Raw file names are found in
There are no alignment or length restrictions on I/O
requests to either block or character devices.
The argument features a bad address.
Invalid argument. EIO. An I/O error occurred.
EPERM Cannot create or delete a ramdisk without write per-
mission on /dev/ramdiskctl.
The device does not support the requested ioctl func-
ENXIO The device did not exist during opening.
EBUSY Cannot exclusively open /dev/ramdiskctl. One or more
ramdisks are still open.
A ramdisk with the indicated name already exists.
Cannot allocate resource for ramdisk. Try again later.
Block device for ramdisk named diskname.
Raw device for ramdisk name diskname
Driver configuration file. (Do not alter).
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Interface Stability | Evolving |
ramdiskadm(1M), fsck(1M), fstyp(1M), mount(1M), newfs(1M),
driver.conf(4), filesystem(5), dkio(7I)
The percentage of available physical memory that can be
allocated to ramdisks is constrained by the variable
rd_percent_physmem. You can tune the rd_percent_physmem
variable in /etc/system. By default, the percentage of
available physical memory that can be allocated to ramdisks
is fixed at 25%.
A ramdisk may not be the best possible use of system memory.
Accordingly, use ramdisks only when absolutely necessary.
Man(1) output converted with