![]() Your output files are also cached, so that you do not wait for them to be written to disk. You can already trust your input files are cached in RAM, the first time they are read. Mechanisms (the page cache and dentry cache) as a dynamically resizable Ramfs is a very simple filesystem that exports Linux's disk caching However as you discovered, this is generally not a useful strategy. This guarantees your input files are loaded in to RAM, and they will not be re-read from the much slower disk drive. You can mount a ramfs filesystem, copy your project into it and work from there. Creating a block device in RAM and initializing it with ext4 avoids this. The cp utility apparently filled the holes on read, but not on write.īoth tmpfs and ramfs may behave differently than a real ext4 filesystem. But when I copied from the ramfs to the destination, my system became unresponsive. This morning, I copied a VM image (150G, but 49G used on disk) to ramfs (I have 128G of RAM). Sparse files can become unsparse when you least expect it. If you put too much in the ramdisk, your system will hang. The df utility does not report space usage: df -h /ramdiskįilesystem Size Used Avail Use% Mounted on But it has its own downsides and surprises: Ramfs is easy to set up, reclaims space once you delete files, and uses RAM more efficiently (the system does not buffer the files because it knows they are in RAM). You are unpacking a large file and you don't want to wear out your SSD.You are doing performance testing and you don't want disk I/O to be a factor (SSD write times can vary a lot).The files you are working with are sensitive (e.g.This is more efficient, but there may be times you want a pure RAM disk: To deallocate the RAM disk, umount it and delete the disk image: umount /ramdiskĪlthough tmpfs and ramfs are more efficient than using a block device, below are some of their downsides. The truncate command creates an empty file of a given size such that it is initialized (i.e. Mount /ramdisk-storage/ramdisk.img /ramdisk Truncate -s 4G /ramdisk-storage/ramdisk.img To deallocate the RAM disk, unmount it and remove the brd kernel module: umount /ramdiskĪlternatively, you can create a block device inside of ramfs: mkdir /ramdisk-storage /ramdisk )) syntax lets you do arithmetic in the shell. ![]() The rd_size parameter is size in kilobytes. The rd_nr parameter specifies how many RAM disks to create (by default, it creates 16, i.e. To create and initialize a 4GB RAM disk: mkdir /ramdisk But it takes more steps to set up, and uses RAM less efficiently. ![]() This approach is more predictable since it creates a real ext4 filesystem and never exceeds the limit you specify. On recent Ubuntu versions, this device does not exist by default, but can be created via modprobe brd. Besides tmpfs and ramfs, another option is the /dev/ram0 block device.
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