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New iMac is slowwww 
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A month or so ago, I bought a new iMac. It's a Retina 4K with a 3.6Ghz Intel Core i3, 8 GB RAM, a Radeon Pro 555 X 2GB graphics card and 1 TB of storage. Problem is that it is very slow to the point where even double-clicking on a Screenshot to open it in Preview can take 10 seconds or longer to open. Could this be because 90% of available 1TB space is being used (mostly for photos stored in 'Photos')? I am in the process of backing up the Photos Library and deleting photos on the HD to see if freeing up more space will help.

I've used Activity Monitor to see if the iMac is being put under strain but it isn't at all. Mostly the CPU is 90% idle when doing basic tasks.

The old iMac was actually 9 years old and nowhere near as slow as this one. If it is not a storage problem, any thoughts on where else I can look to see what the problem is?

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Fri Oct 11, 2019 2:06 pm
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90% disk usage certainly won’t help with the general speed issues, I’d try to clear some disk space and see if that helps.

Are you running the latest system update, Catalina, by any chance? Lots of bugs reported and apps that aren’t fully compatible. If you did a migration from your older iMac, chances are it pulled across some 32-bit applications which are no longer supported on Catalina. 64-bit only on Catalina.

Hope the high disk usage is the cause.

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Sat Oct 12, 2019 10:17 pm
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Is it a 1TB spinning rust or a 1TB SSD?
Sounds like the cpu is waiting for the storage

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Mon Oct 14, 2019 8:21 am
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Thanks for the replies; I'm going to have a mass clearout on the photos and music files and see what that does. It is a 1TB spinning rust so I think making a lot more space available will help.

No, I haven't 'upgraded' to Catalina. Despite the iMac's continual urging to do so I am staying with Mojave because I have seen a couple of reports of problems with other software, including Photoshop.

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Tue Oct 15, 2019 10:27 am
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The best thing you can do is upgrade to an SSD and use the spinning rust for things that don't require the speed, like videos (for playback) or music. Finished photos can also go on spinning rust, but everything you are editing will benefit from an SSD. It certainly made a big difference on my old iMac and on my Windows machines.

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Thu Oct 17, 2019 4:16 am
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Out of interest, what file system does your hard drive use? Is it formatted in the old HFS+ or the new APFS?

Mike Bombich has just released research that shows that APFS is up to 20 time slower than HFS+ on spinning drives, APFS is optimised for SSDs and doesn't bother trying to keep files in sectors that are close to each other, but distributes them randomly all over the drive. This doesn't cause any problems on an SSD, which doesn't have seek times, but it can cause a real slow-down on a spinning drive, because the sectors used aren't in any order that allows them to be read efficiently.

I found that nugget in the current c't magazine.

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Sat Oct 19, 2019 8:49 am
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big_D wrote:
Out of interest, what file system does your hard drive use? Is it formatted in the old HFS+ or the new APFS?


APFS, which might account for some of the slowdown by the sound of it.

I've been clearing space on the HD by backing up photos, etc, so now have 150 GB free. Just to give an example I backed up the Pictures folder and wanted to do a Get Info to see how much space I'd regain. So I did the Get Info request 15 minutes ago and it still hasn't given me the info. It turned out that the file was 4.8 GB which I found out when the iMac was preparing to copy the items over.

The Get Info took 18 minutes in the end.

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Wed Oct 30, 2019 12:51 pm
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It sounds like moving everything off / making a file based backup and then reformatting the drive in HFS+ would be a good move, if you can't switch to an SSD (1TB SSDs are dropping to the 100€ mark over here at the moment).

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Thu Nov 07, 2019 5:36 am
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big_D wrote:
It sounds like moving everything off / making a file based backup and then reformatting the drive in HFS+ would be a good move, if you can't switch to an SSD (1TB SSDs are dropping to the 100€ mark over here at the moment).


Yes, this may be the way forward, thanks.

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Sat Nov 16, 2019 10:51 pm
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I think the latest system, Catalina, requires the system disk to be formatted in APFS doesn’t it, I don’t think you can go back to HFS

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Sun Nov 17, 2019 9:25 pm
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