4 ms·

I believe the prediction is made based on the estimated size of the copy and it doesn't take into account the number of items to be copied. As any seasoned comp

by a2tech 12y ago

I believe the prediction is made based on the estimated size of the copy and it doesn't take into account the number of items to be copied. As any seasoned computer user will tell you, a large number of small files takes longer to copy then a similar sized large file. When the migration wizard is copying a huge number of small files the transfer goes far slower than when it gets into your documents and other large items.

msandford 12y ago
It doesn't seem like it would be TOO hard to get a list of all files to be transferred and sample say 1% of them randomly and from that judge the filesize / filecount statistics and from that make a better estimate. The only reason I could think NOT to do that is that it will take some time. But considering that most of the transfers take an hour or two anyhow, spending 3 minutes up-front to get a reasonable estimate of how much time you have to kill isn't bad. It's more helpful than useless, random guesses.
bradleyland 12y ago
All of that might be true, but it doesn't answer the question: Why isn't the Migration Assistant time prediction algorithm more accurate? Part of this might be the fact that the author is (or at least appears to be) using a traditional magnetic HDD, rather than an SSD. I say this because I've transferred many a MacBook Air over Thunderbolt in 40 minutes for smallish amounts of data. The longest time I've seen MA take was 4 hours for a MacBook Air with a 256 GB SSD (don't recall the utilization). A 10 hour transfer time smells of magnetic platters. The reason HDD vs SSD would impact prediction is that the throughput of an HDD is impacted more severely by a greater number of variables when transferring at the filesystem level than a SSD. Man, that was a mouthful. Stated simply, HDD performance is less predictable than SSD performance. Given the direction Apple is headed with primary storage, I could see them not investing much in tailoring their estimation algorithm toward a technology that is on the wane.

by a2tech 12y ago

msandford 12y ago

It doesn't seem like it would be TOO hard to get a list of all files to be transferred and sample say 1% of them randomly and from that judge the filesize / filecount statistics and from that make a better estimate. The only reason I could think NOT to do that is that it will take some time. But considering that most of the transfers take an hour or two anyhow, spending 3 minutes up-front to get a reasonable estimate of how much time you have to kill isn't bad. It's more helpful than useless, random guesses.

bradleyland 12y ago

All of that might be true, but it doesn't answer the question: Why isn't the Migration Assistant time prediction algorithm more accurate? Part of this might be the fact that the author is (or at least appears to be) using a traditional magnetic HDD, rather than an SSD. I say this because I've transferred many a MacBook Air over Thunderbolt in 40 minutes for smallish amounts of data. The longest time I've seen MA take was 4 hours for a MacBook Air with a 256 GB SSD (don't recall the utilization). A 10 hour transfer time smells of magnetic platters. The reason HDD vs SSD would impact prediction is that the throughput of an HDD is impacted more severely by a greater number of variables when transferring at the filesystem level than a SSD. Man, that was a mouthful. Stated simply, HDD performance is less predictable than SSD performance. Given the direction Apple is headed with primary storage, I could see them not investing much in tailoring their estimation algorithm toward a technology that is on the wane.