Deduplication of file system

FolderSizes also uses highly specialized algorithms for computing these metrics that results in an unparalleled level of accuracy. Now let's run some tests to see how FolderSizes reports and visualizes disk space information for deduplicated volumes. For the purposes of this article, we have created a new local volume designated as drive letter E: in our Windows Server test environment and installed Windows data deduplication services.

However, we haven't yet enabled deduplication on our E: drive. Next, we created a series of four folders on drive E:, each containing an identical set of files. The screenshot below shows the allocation of drive space before deduplication was enabled. As you can see, each of the duplicate folders consumes an equal amount of disk space. Let's also take a look at an arbitrary set of files within one of these duplicate folders.

Again, we haven't yet enabled data deduplication so everything pretty much looks like what you'd expect at this point. Now we'll actually enable data duplication on our E: drive. We configure data deduplication for "general purpose file server" usage and instruct it to deduplicate files older than 0 days so our test files will be affected as soon as possible.

This makes it possible to store more file data in less space on the volume. When new files are added to the volume, they are not optimized right away.

Only files that have not been changed for a minimum amount of time are optimized. This minimum amount of time is set by user-configurable policy. Timeouts occur when networking buffers can no longer handle the demand. Because all services on a network connection share the same buffers, all become blocked. This is usually seen as file activity working for a while and then unexpectedly stalling. File and networked sessions then fail too.

This problem is more likely to be seen when high speed networking is used because the network buffers fill faster. Other tasks might not run properly because of timeouts. This is often encountered with pool scrubs and it can be necessary to pause the scrub temporarily when other tasks are a priority. Diagnose : An easily seen symptom is that console logins or prompts take several seconds to display. Using top can confirm the issue. Solutions : Changing to a more performant CPU can help but might have limited benefit.

A usual workaround is to temporarily pause scrub and other background ZFS activities that generate large amounts of hashing. Useful CLI Commands. Estimates the outcome and DDT table size if a pool were entirely deduplicated. Warning: this can take many hours to complete. The output table is similar to that of zpool status -Dv. These show core deduplication statistics for each pool. The -v option shows disk usage for each individual vdev, which helps confirm that DDT has not overflowed into other disks in the pool.

Healthy pool latencies are generally in the nanoseconds to tens of milliseconds range. If latencies in the seconds or tens of seconds are seen, this indicates a problem with disk usage. This means that certain disks are unable to service commands at the speed needed and there is a large command backlog. Hashing Note expand Deduplication hashes calculates a digital signature for the data in each block to be written to disk and checking to see if data already exists in the pool with the same hash.

Inline deduplication: In this method, the deduplication is run in real-time. Thus, less storage is required. However, since the deduplication process runs as the data comes in, the speed of storage is affected, because the incoming data is checked to identify redundant copies. Data deduplication in Linux is affordable and requires lesser hardware.

The solutions are in some cases available at the block level, and are able to work only with redundant data streams of data blocks as opposed to individual files, because the logic is unable to recognise separate files over many protocols like SCSI, SAS Fibre channel and even SATA. FUSE is a kernel module seen on UNIX-like operating systems, which provides the ability for users to create their own file systems without touching the kernel code. In order to use these file systems, FUSE must be installed on the system.

Most operating systems like Ubuntu and Fedora have the module pre-installed to support the ntfs-3g file system. Lessfs is a high performance inline data deduplication file system written for Linux. Albeiro is open source block level data deduplication software, which was launched by Permabit back in , and is available as an SDK.

Lessfs aims to reduce disk usage where file system blocks are identical, by storing only one block and using pointers to the original block for copies.