Friday, March 12, 2010

Linux RAM Disk: Creating A Filesystem In RAM

Software RAM disks use the normal RAM in main memory as if it were a partition on a hard drive rather than actually accessing the data bus normally used for secondary storage such as hard disk. How do I create and store a web cache on a RAM disk to improve the speed of loading pages under Linux operating systems?

You can create the ram disk as follows (8192 = 8M, no need to format the ramdisk as a journaling file system) :

# mkfs -q /dev/ram1 8192
# mkdir -p /ramcache
# mount /dev/ram1 /ramcache
# df -H | grep ramcache

Sample outputs:

/dev/ram1 8.2M 1.1M 6.7M 15% /ramcacheNext you copy images or caching objects to /ramcache

# cp /var/www/html/images/*.jpg /ramcache
Now you can edit Apache or squid reverse proxy to use /ramcache to map to

DocumentRoot /ramcache
#ErrorLog /var/logs/httpd/images.example.com_error.log
#CustomLog /var/logs/httpd/images.example.com_access.log combined

Reload httpd:

# service httpd reload
Now all hits to will be served from the ram. This can improve the speed of loading pages or images. However, if server rebooted all data will be lost. So you may want to write /etc/init.d/ script to copy back files to /ramcache. Create a script called

mkfs -t ext2 -q /dev/ram1 8192
[ ! -d /ramcache ] && mkdir -p /ramcache
mount /dev/ram1 /ramcache
/bin/cp /var/www/html/images/*.jpg /ramcacheCall it from /etc/rc.local or create softlink in /etc/rc3.d/

# chmod +x /path/to/
# echo '/path/to/' >> /etc/rc.local

A Note About tmpfs
tmpfs is supported by the Linux kernel from version 2.4+. tmpfs (also known as shmfs) is a little different from the Linux ramdisk. It allocate memory dynamically and by allowing less-used pages to be moved onto swap space. ramfs, in contrast, does not make use of swap which can be an advantage or disadvantage in many cases. See how to use tmpfs under Linux.

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