From mboxrd@z Thu Jan 1 00:00:00 1970 From: jnc@mercury.lcs.mit.edu (Noel Chiappa) Date: Thu, 28 Sep 2017 08:53:54 -0400 (EDT) Subject: [TUHS] RFS was: Re: UNIX of choice these days? Message-ID: <20170928125354.CE4E318C088@mercury.lcs.mit.edu> > From: Theodore Ts'o > when a file was truncated and then rewritten, and "truncate this file" > packet got reordered and got received after the "here's the new 4k of > contents of the file", Hilar[i]ty Enused. This sounds _exactly_ like a bad bug found in the RVD protocol (Remote Virtual Disk - a simple block device emulator). Disks kept suffering bit rot (damage to the inodes, IIRC). After much suffering, and pain trying to debug it (lots of disk writes, how do you figure out the one that's the problem), it was finally found (IIRC, it wasn't something thinking about it, they actually caught it). Turned out (I'm pretty sure my memory of the bug is correct), if you had two writes of the same block in quick sucession, and the second was lost, if the first one's ack was delayed Just Enough... They had an unused 'hint' (I think) field in the protocol, and so they recycled that to be a sequence number, so they could tell ack's apart. Noel