Re: pkg/46529: ntfs-3g appears to be rate-limited

["Aaron J. Grier via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/46529; it has been noted by GNATS.

From: "Aaron J. Grier" <agrier%poofygoof.com@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: pkg/46529: ntfs-3g appears to be rate-limited
Date: Wed, 6 May 2026 11:40:05 -0700

 you are absolutely correct, the baseline is all zfs cache behavior on
 the backing side, and doesn't represent actual disk I/O.
 
 looking on the back-end I see zvol iostat showing ~120MB/s but no
 activity on the disks in the array, and no blinking lights on the drives
 themselves.  since the disk image is on a sparse (and compressed) ZFS
 volume, this has to be expected.
 
 I disabled my swap wedge and dding from it generated actual disk
 activity, but since the backing store is sparse, as soon as reads moved
 past the small amount of existing swap data, sparse handling kicked in
 and the rest of the wedge data was fulfulled without any disk I/O.
 
 I don't have an easy way to get actual USB passthrough on the system (it
 lives in a rack and has no easy-access USB ports), so I'm not sure how
 to get a good baseline out of this.
 
 here's an iostat snippet from the NetBSD side while reading through ntfs-3g:
 
 device  read KB/t    r/s   time     MB/s write KB/t    w/s   time     MB/s
 ld0          2.00  38431   0.58    75.06       0.00      0   0.58     0.00
 ld0          2.00  34170   0.69    66.74       0.00      0   0.69     0.00
 ld0          2.00  37623   0.70    73.48       0.00      0   0.70     0.00
 ld0          2.00  34487   0.79    67.36       0.00      0   0.79     0.00
 ld0          2.00  35610   0.87    69.55       0.00      0   0.87     0.00
 ld0          2.00  39171   0.70    76.51       0.00      0   0.70     0.00
 ld0          2.00  35614   0.81    69.56       0.00      0   0.81     0.00
 ld0          2.00  38249   0.71    74.70       0.00      0   0.71     0.00
 ld0          2.00  40597   0.52    79.29       0.00      0   0.52     0.00
 ld0          2.00  36121   0.79    70.55       0.00      0   0.79     0.00
 
 the VM back-end is all cached at this point, but it's not NetBSD's
 buffercache.  
 
 the original problem was that ntfs-3g was slow, which I'm definitely no longer
 observing.  I'm satisifed now, and feel like I'm beating a dead horse at this
 point, given the original ticket was filed in 2012.
 
 ready to close this one if you are.