Unable to ssh; super dim, blinking green led

[fvgs]

I commissioned my Pi as a BitTorrent client and have had it running headless for a few days. I rely on ssh over LAN to connect to it. It has been mostly idle, in part because I was troubleshooting a separate issue. But a few hours ago I started downloading a 40GB torrent on the Pi and left it doing that. The only storage it has is a 64GB microSD card. Even with the full torrent downloaded, there should be at least 10GB of space left on the card. That said, there's no way it could have finished the download already. As I learned recently, writing to the sd card in this fashion is a major bottleneck. Anyway, I tried to ssh in to the Pi to check its progress and was unable to do so. I was met with the following error:

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Connection reset by <ip address> port 22

Running ssh with -vvv shows my computer connecting to the Pi, but the connection is reset/closed (as seen above) after the following occurs:

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debug1: SSH2_MSG_KEXINIT sent

Additionally, I looked at the leds on the Pi and, while the red led is steady and strong, the green one has just a tiny speck that is flashing, nothing more. What I would expect is for the green led to be flashing strongly to indicate writing the torrent download to the sd card.

My hypothesis is that something went wrong with the sd card and it is currently in an unreadable and unwritable state. That would explain the abnormal green led behavior. Likewise, if sshd is unable to read its config files from the sd card, it would explain why sshd is reseting/closing the connection when I try to ssh in.

That said, I'm wondering if anyone knows what (if anything) the green flashing speck is meant to indicate? Furthermore, does my hypothesis seem sound? If so, my next action is to unplug the Pi (no harm done at this point) and see if it'll boot. But if my hypothesis is incorrect, I would prefer not to unplug it if there is a better alternative (monitor+keyboard not an option).

UPDATE: I went ahead and unplugged the Pi and plugged it back in. It proceeded to boot up and I was able to ssh in. A review of some files in /var/log shows no log entries during the period where I observed my Pi to be in this malfunctioning state. Though, I'm not that experienced when it comes to linux systems, so it's possible I'm not looking in the right places. But so far, this supports the theory that some issue occurred with the sd card and it was in an unreadable/unwritable state. The question then remains, HOW did this happen? The likely culprits are deluged and/or the sd card. However, I don't presently have enough evidence to produce a satisfactory theory for how. The obvious factor is that deluged was writing heavily to the sd card. But this alone isn't a satisfactory explanation. Moreover, it's an important question to answer since it could happen again which would mean me getting locked out of my server and having to physically unplug it which could risk further corruption depending on the extent of the inaccessibility of the sd card. Any help with figuring out what is going on is much appreciated.

[fvgs]

After unplugging the Pi, booting it up again, and leaving Deluge to continue the download, I have run into the same issue again. That is, I am unable to ssh into the Pi and the green led is as described above. This is now the second time it has happened, so it seems to occur some time after Deluge has been running for a little while. To be clear, I don't suspect this issue has anything to do specifically with Deluge. Rather, the problem seems to be with one or both of the Pi and the sd card.

I'm hoping someone can offer guidance as to what might be the cause and how to fix this so it doesn't keep happening.