I’ve a Mac operating 10.14 as a file server. I’ve been copying recordsdata to it and at present I seen some very unusual caching/buffering habits. The drive is an exterior USB 2 HDD, so it tops out at round 40MB/s (and transfers to the share are the identical). At the moment the community velocity out of the blue went as much as round 100 MB/s (maxing out ethernet), then it simply stops. Taking a look at iStat menus on the server, I discover that smbd would not really begin writing knowledge to the disk till what I assume is its write buffer getting stuffed up, then it begins writing the info. This causes the switch on my finish to freeze (clearly) however it additionally causes all the share to freeze for my laptop, so interacting with it in any manner leads to a beachball.
Not solely that, however as a result of this delays the precise write-back to the disk, it takes far longer, because it spends time doing nothing ready for this buffer to refill, then blocks the switch and slowly writes the info it might (ought to) have been writing all alongside. Then it cycles once more, it stops writing, waits for the buffer to fill, then begins writing once more. The buffer is someplace above 1.6 GB or so, as that was the smallest file I had and it copied all of it earlier than it even began writing to the disk.
I’ve not modified something, I’ve been copying knowledge to it for a couple of days now and I’ve by no means seen this habits earlier than (nor have I ever seen this habits at any level previously, even with small transfers it might instantly write them to the disk, on this laptop or some other, I discover it odd that something would permit that a lot knowledge to stay unwritten). It would not appear to matter if I exploit Finder or cp on the shopper, nor does it appear to matter if I exploit SMB or AFP.
Talking to the unwritten knowledge half, whereas energy outages should not the most important concern, the truth that my knowledge is not really being written to the disk till a lot later is regarding as effectively.
