08-27-2012
There was a time when you used to multipy by 2 or 3 (HPUX9-HPUX10...) then came the lowcost of RAM with servers supporting a lot and so some configuration went on with loads of RAM but then we saw issues like "How come I get < no more memory to load...> when I have 16GB of RAM and we seem to use only 12?> etc... Im glad to see HP changed it point of vue to swapsize=RAMsize, but it is only to not see anymore the previous in support...
As jlliagre explains, only you can answer for we dont know what you are running, nor how much disks space you have nor the type (yes it has its importance...). For performance I suggest if you were to create 32 GB swap device to create 4 of equal size...(load balancing...)
Tell us more what you are trying to achieve, we give you our point of vue, tuning is the art or compromize (which is the best for you?) knowing what you need to achieve is the way to go, you can finish like me 10 years ago having tuned a K360 with only 2GB RAM to run 6 oracle instances (of three diff versions...) with a sybase, and ftp server 24/24 and approx 600 users concurrent... without any performance issues...
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bcopy(9F) Kernel Functions for Drivers bcopy(9F)
NAME
bcopy - copy data between address locations in the kernel
SYNOPSIS
#include <sys/types.h>
#include <sys/sunddi.h>
void bcopy(const void *from, void *to, size_t bcount);
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI).
PARAMETERS
from Source address from which the copy is made.
to Destination address to which copy is made.
bcount The number of bytes moved.
DESCRIPTION
bcopy() copies bcount bytes from one kernel address to another. If the input and output addresses overlap, the command executes, but the
results may not be as expected.
Note that bcopy() should never be used to move data in or out of a user buffer, because it has no provision for handling page faults. The
user address space can be swapped out at any time, and bcopy() always assumes that there will be no paging faults. If bcopy() attempts to
access the user buffer when it is swapped out, the system will panic. It is safe to use bcopy() to move data within kernel space, since
kernel space is never swapped out.
CONTEXT
bcopy() can be called from user or interrupt context.
EXAMPLES
Example 1: Copying data between address locations in the kernel:
An I/O request is made for data stored in a RAM disk. If the I/O operation is a read request, the data is copied from the RAM disk to a
buffer (line 8). If it is a write request, the data is copied from a buffer to the RAM disk (line 15). bcopy() is used since both the RAM
disk and the buffer are part of the kernel address space.
1 #define RAMDNBLK 1000 /* blocks in the RAM disk */
2 #define RAMDBSIZ 512 /* bytes per block */
3 char ramdblks[RAMDNBLK][RAMDBSIZ]; /* blocks forming RAM
/* disk
...
4
5 if (bp->b_flags & B_READ) /* if read request, copy data */
6 /* from RAM disk data block */
7 /* to system buffer */
8 bcopy(&ramdblks[bp->b_blkno][0], bp->b_un.b_addr,
9 bp->b_bcount);
10
11 else /* else write request, */
12 /* copy data from a */
13 /* system buffer to RAM disk */
14 /* data block */
15 bcopy(bp->b_un.b_addr, &ramdblks[bp->b_blkno][0],
16 bp->b_bcount);
SEE ALSO
copyin(9F), copyout(9F)
Writing Device Drivers
WARNINGS
The from and to addresses must be within the kernel space. No range checking is done. If an address outside of the kernel space is
selected, the driver may corrupt the system in an unpredictable way.
SunOS 5.10 4 August 2003 bcopy(9F)