On Friday 26 June 2020 21:58, Rupert Gallagher via rsync <rsync@lists.samba.org> wrote:
> Hello, > > As disks are slow and rsync reads and writes so much that for the bus this is > the equivalent of context switching galore, would it be possible to use RAM > as a buffer? Say, you have 10GB of spare RAM, rsync uses the bus to its peak > for reading 10GB, then again for writing it down. This would be more > efficient than lot of small read/write operations. > > Thank you Current task: rsync 752 GB source disk Writing speed: 77 MB/s Reading speed: 97 MB/s target disk Writing speed: 117 MB/s Reading speed: 99 MB/s Actual time: 380 min (6.3 hours) to copy 648 GB Actual speed: 28 MB/s (648/380 = 1.7 GB min =~ 1700MB min / 60 min = 28MB sec) Potential speed Since both disks are on same bus, first we saturate the bus when reading, then we saturate the bus when writing. reading time: 752 GB =~ 752000 MB / 97 MB/s =~ 7752 sec = 2.2 hours writing time: 752 GB =~ 752000 MB / 117 MB/s =~ 6427 sec = 1.7 hours In summary, the task could be completed in 4 hours instead of 8. If the disks were on a different bus, and RAM would be refilled while writing on disk, the task could be completed in 2 hours. -- Please use reply-all for most replies to avoid omitting the mailing list. To unsubscribe or change options: https://lists.samba.org/mailman/listinfo/rsync Before posting, read: http://www.catb.org/~esr/faqs/smart-questions.html
