![]() It spends most of its time sleeping, but it is also responsible for checking block hashes and deciding which blocks to write.ĭelta block size, read/write buffer sizes - all these are in the. ![]() But if they differ, than it's that 1 in metamillion chance of block hash collision and so it scrapes everything and re-copies file in full.Īnd one more core is reserved for the dispatcher thread that directs buffers between the reader, hasher and writer. If they match, everything is OK and the file is unchanged. So in v2 if the copier sees that all block hashes remained unchanged, it compares freshly computed file hash against the hash from the previous run. That's the cases when a changed block just happens to end up with the same hash as before. This is new in v2 and it's a safeguard that detects false negatives. One more core is used to compute running file hash. Copier reads 32 blocks per request, so it has 32 block hashes to compute and these are distributed across all available cores, less two (but obviously at least one core if there's less than two). Each block is hashed as a single operation. multiple hashes, each on a single or on multiple cores) ?īy default, delta blocks are 32K each. Both are my companies that I use for legal and accounting purposes.ġ) Hashing - is only one hash at-a-time done on multiple cores, or is each stage of the pipeline multi-threaded (ie. Please welcome Pipemetrics SA of Switzerland. Yaletown Software Design of Canada is no more. Switched to signing releases with Pipemetrics SA certificate ![]() 13%, but then looks at effective copying speed and adds decimal points if the copying is slow so to always show some activity with slower copies. Interestingly, the app starts with a simple percentage, e.g. The overhead of this step is minimal, but it still can be turned off in the configuration if needed. More specifically, it now correctly replicates "last modified" timestamps - this is done as a post-processing step, once all files are copied and updated. With all things combined, the net effect is that the delta copier now runs as fast as robocopy *despite* the fact that it does quite a bit more than just read/write things.īeta 31 now copies folder timestamps. This release also includes highly-optimized versions of the actual hashing code (courtesy of OpenSSL) and this alone speeds up hashing step by 20-30% compared to older versions. And so this carousel spins until there's nothing more to read, hash and write. Then, once a write request is completed, the block is shuffled back into the reader, which uses it to issue another read request. Then, once a block is hashed, it is forwarded to the writer, which compares block hashes to those from the previous run and issues write requests for blocks whose hashes changed. Hashing module uses all available CPU cores, so the more you have the faster the hashing will be. As these requests are completed by the OS, read data is forwarded to the hashing module, which is a purely computational task. The copying is started by seeding reader with a bunch of read requests. Delta copier forms a copying pipeline out of reader, hasher and writer modules. The asynchronous nature of new copier comes *especially* handy when dealing with delta copying. As a side note, robocopy is actually *really* good performance-wise (but it still appears to be synchronous on the inside). In particular, this delivers a speedup of 10-15% over robocopy with bulk (non-delta) copying. This is highly beneficial when data is copied between two physical disks as the OS can be kept busy reading and writing data at the same time. It now works in a fully asynchronous fashion - it can issue multiple read and write requests and then let Windows complete them in the background. I have rewrote the part that handles copying of files. This is done not to mess up drive's original SysVolInfo that contains drive-specific data and that typically should not be touched. ![]() The app now ignores "System Volume Information" directory, when the backup location is pointing *at the root* of the drive. Both should be resolved now.Īdded handling of "System Volume Information" folder Incidentally, slow start was a cause of a couple of other problems - the inability to switch to the service mode and the program window taking few minutes to show up when running in service mode. The speed-up is significant and in many cases it is as high as 10 times if not more. I reviewed what the app is doing at the launch time and then trimmed, delayed and rearranged a lot of things so that the main program window is now displayed as soon as possible. Significantly improved program start-up time ![]()
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