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

[Max Neupert]

hi,
some sources suggest that there is no or little advantage to use a  
ramdisk in os x because the system caches data which has frequent  
access anyway.
so a ramdisk can be counterproductive in a cenario where you have  
little ram:
lets say you have one gig memory. 300 mb are used by some  
applications which are open, and another 300 by the system. now you  
have a video in your ramdisk of also 300. the system tries to cache  
it because it wants to accellerate but can't allocate enough anymore  
and data will be swaped on the harddisk..
so you end up with less performance and more harddrive access because  
of the ramdisk..

i'm curious about your findings.

greetings, m.


http://lowendmac.com/x-basics/02/0201.html
http://www.kernelthread.com/forums/viewtopic.php?t=138

Am 30.07.2007 um 10:08 schrieb 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"
>
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