El Capitan can not see an external drive

Same problem here. I have two macs, both running El Capitan. Two External HDs, a portable one and a backup plus. The computer seens to recognize something on the firewire port, but can`t read nothing :/

It`s in portuguese, it says "unknown device"

My drive has been formated and worked fine previously. It stopped working only after the upgrade. Below you can see the actual drive configuration - the drive is Encrypted and I wonder if it has something to do with it. Weird thing is that I can't now format/partition it or anything else - not that I'd want to do so but I did try it. When I click on Mount nothing happens, should normally prompt me for password but it does not do so.

Seagter external HDD sorted.

I had two External HDD which worked with Yosemite but went missing under El Capitan. I did get the Seagate ext HDD working by doing the following:-

Click the Apple Logo / System Preferences / right click NTFS for Max OS X at the bottom and remove it. Go to :-

http://www.seagate.com/gb/en/support/downloads/item/ntfs-driver-for-mac-os-maste r-dl/ and downlopad the new El Capitan update.

Hope this helps.

Have not yet managed to get the Octigen HDD working though.

I am having the same issue, pretty sure it is not a problem with the drive but instead with the version of OS as I was able to use the drive before.

My issue is on 2011 MacBook Pro 17, and I used the drive as a backup that I can't now access 😟

BTW my drive is encrypted, and it is NOT prompting me to enter the Password when I connect it.

Apple support can you look at this issue?

if the drive shipped with the NTFS file format the mac OS will not allow you to write on it and the 3rd party software installed by Seagate may not be compatible with Mac OS 10.11

If older Seagate software is on it you can remove that software, then reinstall using the software on Segates site which may or may not be 10.11 compatible either.

if you do not need to use the drive with windows reformat (backup before you wipe it out) the drive using Mac Extended (Journaled) from the Disk Utility.

This will give you full access to the drive and store the file permissions.

NTFS is for windows, there is no benefit to using it on a mac unless you plug it directly into a Windows computer.

I just started having the same issue with my MacMini. As of last night, El Capitan no longer recognizes my (relatively new) USB external 3tb Seagate drive, even though it does recognize my older 1tb Seagate drive. When I check under 'About This Mac" it sees the drive enclosure, a Newer Technology Ministack, but not the drive.

I tried attaching the 3tb drive to a MacBook Pro that's still running Yosemite and the MacBook Pro recognizes it just fine.

Odd part is, it was reading and writing just fine a day or two ago.

Update:

I've also been getting alerts that a drive was removed incorrectly. After posting the previous message I was able to download the Yosemite installer but when I tried to create a boot disk, using DiskMaker X, the first attempt failed. Oddly enough the second attempt worked and I noticed my computer was then able to recognize my hard drive.

Then just a few minutes ago I got the "Disk Removed" alert and once again, my computer is failing to recognize the hard drive.

Was panicking yesterday when I lost access to my drive because I have years and years of stuff in my almost 1-year old Seagate BackUp Plus (3TB). I had been slowly transferring data from an older seagate model. Will have to look for a Yosemite machine to verify the integrity of my data.

Is Apple ever going to do anything about this? Is this a manufacturer specific problem or are all external drives going to be susceptible to this bug?

I am getting similar errors with the sd card for my e-reader. I don't have a built-in sd card reader, so I keep it in the e-reader, and I connect both.

I get spurious "not readable" messages" about the sd card the first time I connect, so have to eject both, then plug them back in again, and can transfer files the econd time I connect. I can then eject both, get the "not ejected properly" message a couple hours later, and repeat the cycle the next time I connect.

Latest OS update 10.11.2 did NOT resolve this issue. Very frustrating to have a 3TB hard drive sitting idle since my mac cannot connect to it using El Captain. Considering downgrading back to Yosemite

I am not sure if I help someone with this but I just figured out this:

I bought a WD MyBook 6TB with USB3 for encrypted TimeMachine backups of my iMac (27-inch, Mid 2010) with USB2 running on OS X 10.11.2. Non-encrypted backups aren't a problem, but as soon as I turn on encryption the drive gets unmounted and I see this error: "The disk you inserted was not readable by this computer." Happily I also have a MacBook Air (11-inch, Mid 2013) with USB3 running on OS X 10.11.2 as well. When I erase (and format) the disk with Encryption on my MacBook and reconnect the external drive to my iMac the error has gone and I can create an encrypted TimeMachine backup of my iMac.

SO my problem is a seagate 1tb hard drive on a brand new macbook. I have backed up on it before. Now it won't recognise it. It even says there are backups on the drive but cannot see it. The drive works perfectly on an older macair - not running el capitan. Any clues?

El Capitan system was working just fine on my Mac Mini. Had made backups to external HD with Carbon Copy Cloner without any problem. Suddenly started getting "device improperly disconnected" error messages during CCC backups. Now external HD not recognized. Reset SMC and PRAM. Disk Utility doesn't recognize disk and Terminal doesn't list disk.

Really upset thinking I'd corrupted directory and lost all my backups until I plugged into MacBook Pro with Mountain Lion and everything mounts, displays, opens and works just fine.

BUT I still cannot make backups of El Capitan system UNLESS running 10.9.5 or greater, so I'm still screwed by crAPPLE, because I'm not going to pay for software upgrades in order to upgrade the MacBook Pro OS. Would still be running it but POP3 stopped working, and had to switch to IMAP which doesn't work WAS NEVER FIXED on Mountain Lion. So I upgraded to El Capitan on the Mac Mini.

Had the same disk drop on Mountain Lion some years ago but it was resolved. Not sure how. Using Startech hot swap dual drive with Seagate green drives. Startech had no real answer, other than make sure to NOT check "put hard drives to sleep when possible" in Energy Saver of System Prefs. After installing Please Sleep and adding CCC to exceptions in prefs, problem went away on MacBook Pro Mountain Lion system. Was running same system on Mac Mini with no problem. Migrated everything from that system to El Capitan and didn't have any problems for several weeks until now.

Other annoying issues include duplicate alerts in iCal which I could only resolve by deleting imported calendar entries and recreating them.

My experience is there's always something. Two steps forward and one step backward is the crApple m.o., all the while touting typical "progress" and latest and greatest.

After spending yet more hours online digging around, I tried 2 other things - ran Kext Utility (didn't work), booted into Safe Mode, then rebooted (did work).

Could not boot into SM the usual way by holding down Shift key at startup.

Had to use Terminal to set to always boot SM, then after booted in SM, set terminal to not always boot SM.

External HD now mounts on desktop again.

Will update whether or not I can run CCC backup without connection to external HD being dropped after I attempt that.

For now, I'm simply celebrating having disk mounted again.