![testdisk image.dd testdisk image.dd](http://winitpro.ru/wp-content/uploads/2017/04/select-drive.jpg)
As you may have guessed, we get such high numbers because of I/O caching that OS cleverly applies when working with files.Ĭaching is done in such a way that kernel would cache I/O as long as it has unused memory. Slightly better I/O for reading is always expected, but such a dramatic improvement is usually false. Problem 2: even if we remove the oflag=direct, results seem to be too good to be true: :~ $ dd if=./test of=/dev/zero bs=512k count=2048ġ073741824 bytes (1.1 GB) copied, 0.159449 s, 6.7 GB/s Problem 1: you get an error if you attempt direct I/O (oflag=direct) with a virtual device like /dev/zero: :~ $ dd if=./test of=/dev/zero bs=512k count=2048 oflag=directĭd: failed to open '/dev/zero': Invalid argument If you try running it though, you’ll have 2 problems. test file: :~ $ dd if=./test of=/dev/zero bs=512k count=2048 oflag=direct If you apply logic and reverse the if and of parameters from the previous example, you will arrive at the following dd command testing the speed of reading from.
![testdisk image.dd testdisk image.dd](https://korben.info/app/uploads/2016/12/test5-650x467.jpg)
Similar results may be achieved using a software RAID from HDDs. That’s a pretty impressive throughput! If the filesystem we’re testing this on is hosted on a single disk, it must be an SSD one. In this example, I’m creating a 1GB file using a fairly large block size of 512KB: :~ $ dd if=/dev/zero of=./test bs=512k count=2048 oflag=directġ073741824 bytes (1.1 GB) copied, 3.11501 s, 345 MB/s That’s why using is one of the easiest ways to understand the storage you’re working with.
#Testdisk image.dd install
Dd command, that is pretty much guaranteed to be pre-installed on your Linux or Unix server, can be used to quickly get an understanding of the I/O capability of available storage.Īlthough there are specialised file processing and I/O benchmarks, you may not always have the time or permission to install additional packages.