[PD] [Gem] pix-native? [RAM disk]

[Derek Holzer]

vade wrote:

 > If you can sustain the datarates for the number of streams you want the
 > uncompressed will always win with ease of CPU decoding, at the expense
 > of being NASTILY hard on your drives.

Chris also suggested using a RAM disk, which would save a lot of wear 
and tear on the HD in the case of uncompressed video.

I did some research on RAM disks for OS X. Seems like you can skip 
buying a license for Rambunctious and just use the command line. I 
promised Baruch that I would post on this, so some recipes follow, 
copied from various internet sources...

best,
d.

*****************

#!/bin/sh
NUMSECTORS=524288
# 64mb = 131072
# 128mb = 262144
# 256mb = 524288
# 512mb = 1048576
# 1gb = 2097152
mydev=`hdid -nomount ram://$NUMSECTORS`
newfs_hfs $mydev
mkdir /tmp/ramdrive
mount -t hfs $mydev /tmp/ramdrive

Save the file with a name like 'mkramdisk.sh', and give it executable 
permissions:

chmod 755 mkramdisk.sh

Run it. Voila. This script is right out of the man page for hdid. You 
can also read about doing this at

http://www.kernelthread.com/mac/osx/arch_fs.html


********

Creating a RAM disk was easy in 9, and, until now, "undocumented" in X. 
There is a utility called "ramBunctious" (available at VersionTracker) 
that brings this functionality back to X (well, at least it puts a GUI 
on it).

For those of you interested in how this works from the command line, its 
pretty simple. First, create a read/write disk image (you can do this in 
Disk Copy). Next, create the /dev entry for RAM using the hdid tool. 
Finally, copy the contents of the disk image to the RAM /dev entry and 
mount it. Because the disk image is mounted from the /dev entry, any 
changes occur in RAM. Here are the Terminal commands:
[First, calculate the number of 512K blocks you need: numblocks = (image 
size in MB) * 2048; for example: 5MB = 10240 blocks]


% hdid -nomount ram://numblocks
[result: /dev/disk1]

% dd if=/path/to/image/file.dmg of=/dev/disk1 bs=512
[result:2866+0 records in
2866+0 records out
1467392 bytes transferred in 1 secs (1467392 bytes/sec)]

% hdiutil mount /dev/rdisk1

You need to change the "1" in disk1 and rdisk1 to whatever number is 
returned by the first command.

Please be sure to check out ramBunctious; it has excellent documentation 
on the state of RAM disks in X and when you should/should not use them.

The reason I mention it here is because it could have a huge positive 
impact on the functionality of a bootable X cd.



**************



How to create a RAM disk on OS X

32768 = size in sectors (16MB in this case, a sector is 512 bytes)

$ hdid -nomount ram://32768
/dev/disk1
$ newfs_hfs /dev/disk1
$ mkdir /tmp/ramdisk1
$ mount -t hfs /dev/disk1 /tmp/ramdisk1

To unmount:

hdiutil detach /dev/disk1

to osx files tiger ramdisk ram disk by peter on Thu Mar 30 16:25:22 EST 2006

**************

I have thrown together a quick script for anybody that wants to create a 
ramdisk regularly. It's flexible enough for me, but can be edited to 
offer more options (if u know a little .sh scripting). The disk is 
dynamicly named and will show up on the desktop when the script is 
finished. Unmounting can be done as any drive in the finder. The major 
differences between my and the above approach is that I use diskutil to 
mount the created drive, so Finder likes it better, and i give the 
volume a label, so it can be better recognized by the user ...

Here it is:

Leila:~ samynew[14:30:55]$ cat ramdisk
#!/bin/bash
if [ -n "$2" ]; then ARG_ERR=ERR; fi
if [ -z "$1" ]; then ARG_ERR=ERR; fi
if [ -n "$ARG_ERR" ];
then
echo 1 argument: size in MB
exit
fi
MB_SIZE=$1
let "MB_SIZE *= 2048"
echo Creating ${MB_SIZE} 512-blocks ramdisk
CREATED_RAMDISK=`hdid -nomount ram://${MB_SIZE}`
echo New block device: ${CREATED_RAMDISK}
DISK_NAME=`basename ${CREATED_RAMDISK}`
echo Creating volume with label: ${DISK_NAME}
newfs_hfs -v ${DISK_NAME} /dev/r$CREATED_RAMDISK
echo Mounting in /Volumes/${DISK_NAME}
mkdir /Volumes/${DISK_NAME}
diskutil mount ${CREATED_RAMDISK}

Make sure it's chmodded to be executable: chmod u+x ramdisk
Run as: ./ramdisk <size-in-MB>





****************



For those of you interested in how this works from the command line, 
it's pretty simple. First, create a read/write disk image (you can do 
this in Disk Copy). Next, create the /dev entry for RAM using the hdid 
tool. Finally, copy the contents of the disk image to the RAM /dev entry 
and mount it. Because the disk image is mounted from the /dev entry, any 
changes occur in RAM. Here are the Terminal commands:

First, calculate the number of 512K blocks you need: numblocks = (image 
size in MB) * 2048; for example: 5MB = 10240 blocks. Open a terminal and 
type:

% hdid -nomount ram://numblocks
[result: /dev/disk1]

Replace numblocks with the number you calculated in the first step. Next 
type:

% dd if=/path/to/image/file.dmg of=/dev/disk1 bs=512
[result:2866+0 records in
2866+0 records out
1467392 bytes transferred in 1 secs (1467392 bytes/sec)]
% hdiutil mount /dev/rdisk1

You need to change the "1" in disk1 and rdisk1 to whatever number is 
returned by the first command.




*****************

Espérance DV
Esperance DV is a module for System Preferences making a RamDisk. You 
can place temporary files for speed saving video, speed recording a lot 
of pictures, building your application with xCode,... RamDisk is the use 
of a part of read-write memory (RAM) as a hard disk.

http://www.mparrot.net/index.php?page=downloads&lang=en


-- 
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 161:
"Trust in the you of now"