Date: Wed, 4 Oct 2017 10:58:01 -0700 From: Freddie Cash <fjwcash@gmail.com> To: javocado <javocado@gmail.com> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: lockup during zfs destroy Message-ID: <CAOjFWZ7ohEkTvK-jRUOjFmTaaOOViJUrtQWKR8oJyo-CV=%2Bk6Q@mail.gmail.com> In-Reply-To: <CAOjFWZ54hB_jRaSQ8NX=s214Km9o%2BN=qvnQehJykZbY_QJGESA@mail.gmail.com> References: <CAP1HOmQtU14X1EvwYMHQmOru9S4uyXep=n0pU4PL5z-%2BQnX02A@mail.gmail.com> <CAOjFWZ54hB_jRaSQ8NX=s214Km9o%2BN=qvnQehJykZbY_QJGESA@mail.gmail.com>
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On Wed, Oct 4, 2017 at 9:27 AM, Freddie Cash <fjwcash@gmail.com> wrote: > On Wed, Oct 4, 2017 at 9:15 AM, javocado <javocado@gmail.com> wrote: > >> I am trying to destroy a dense, large filesystem and it's not going well= . >> >> Details: >> - zpool is a raidz3 with 3 x 12 drive vdevs. >> - target filesystem to be destroyed is ~2T with ~63M inodes. >> - OS: FreeBSD 10.3amd with 192 GB of RAM. >> - 120 GB of swap (90GB recently added as swap-on-disk) >> > > =E2=80=8BDo you have dedupe enabled on any filesystems in the pool? Or w= as it > enabled at any point in the past? > > This is a common occurrence when destroying large filesystems or lots of > filesystems/snapshots on pools that have/had dedupe enabled and there's n= ot > enough RAM/L2ARC to contain the DDT. The system runs out of usable wired > memory=E2=80=8B and locks up. Adding more RAM and/or being patient with = the > boot-wait-lockup-repeat cycle will (usually) eventually allow it to finis= h > the destroy. > > There was a loader.conf tunable (or sysctl) added in the 10.x series that > mitigates this by limiting the number of delete operations that occur in = a > transaction group, but I forget the details on it. > > Not sure if this affects pools that never had dedupe enabled or not. > > (We used to suffer through this at least once a year until we enabled a > delete-oldest-snapshot-before-running-backups process to limit the number > of snapshots.)=E2=80=8B > =E2=80=8BFound it. You can set vfs.zfs.free_max_blocks in /etc/sysctl.conf= . That will limit the number to-be-freed blocks in a single transaction group. You can play with that number until you find a value that won't run the system out of kernel memory trying to free all those blocks in a single transaction. On our problem server, running dedupe with only 64 GB of RAM for a 53 TB pool, we set it to 200,000 blocks: =E2=80=8Bvfs.zfs.free_max_blocks=3D200000 --=20 Freddie Cash fjwcash@gmail.com
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