Defective Cache

[DanielSB]

Hi there

Been using uTorrent (old build) on WINE for awhile now without any problems. Over the last couple of weeks, I've been using Windows 7, though, so I've had some time to use the newer versions of uTorrent.

The first one I installed, was the stable release as linked to on the front page, version 2.2.1.

I used it for a while, but one day I downloaded a bunch of torrents, and quickly found the cache filled, "Disk Overloaded 100%" showing up in the status bar, and no amount of tweaking that I could do would fix this. I tried checking on and off different options on the cache page, even increasing the cache size up to a staggering 1GB. This just meant the cache filled steadily up to 1GB, then gave the "Disk Overloaded 100%" message once more. Closing the application would leave utorrent.exe in the running apps list in taskmanager, with it having allocated 1+ GB mem, ever so slowly releasing it at what looked to be maybe 5 kB/sec.

I then tried downloading the 3.0 beta instead, and for a while everything was dandy. Half an hour ago, I downloaded a new torrent (http://www.btmon.com/Other/Other/Monster_House_2006_BDRip_1080p_Rus_Eng.torrent.html), which fired up at ~4½ MB/sec. My now 512MB big cache was quickly filled, and I found myself in the exact same situation. "Disk Overloaded 100%" - resident utorrent.exe active in task manager after being closed, having to force-kill the process.

Did a reboot just for the sake of it, and tried again. Same thing.

Target volume is an ICH10R RAID-5 array of four drives. Quick test copying a very large file from the array to an SSD and back shows ~100MB/sec reads, ~60MB/sec writes.

Weird thing! When I started writing this post, uTorrent's cache was filled, the app downloading at ~1 kB/sec. Now, it's apparently all happy again, with an almost empty cache, downloading at 4.5 MB/sec.

Something's amiss with the cache... Please tell me what info you need, what tests I should run.

[DreadWingKnight]

Preallocate on with sparse files off?

[DanielSB]

Yes! Is it waiting for Windows to finish allocation???

[DreadWingKnight]

The preallocation of a non-sparse file is EXTREMELY disk intensive to the point that even a RAID0 stripe of SSDs have a hard time keeping up.

I personally run with sparse on, and don't get this behavior, even on multi-GB files (where the problem comes up most often).

[DanielSB]

Well, that makes perfect sense, then! I was actually wondering why the cache wasn't being increased, as I had enabled the option to increase cache when disk thrashing. Waiting for Windows to finish pre-allocation obviously isn't disk thrashing, so the cache just remained as it was. Would be very nice with a second option, such as "Temporarily increase disk cache while waiting for file pre-allocation to complete" so that downloads wouldn't be paused when starting new, large, downloads. I have 12 GB of mem, and while I wouldn't appreciate a permanent cache size of, say, 10 GB, uTorrent eating up most of otherwise unutilized memory while waiting for file allocation to finish would be perfectly fine with me

About sparse files - AFAICT, that pretty much cancels out the effect you get through pre-allocation. A sparse doesn't use any blocks on disk until they're written to, and so, their allocation doesn't happen until they're actually written, and fragmentation isn't prevented.

Thanks for your help!