Date: Wed, 5 Aug 2020 00:32:26 -0400 From: Ryan Moeller <ryan@ixsystems.com> To: "PK1048.COM" <info@pk1048.com> Cc: Grant Gray <grant@gray.id.au>, freebsd-fs <freebsd-fs@freebsd.org>, George Wilson <george.wilson@delphix.com> Subject: Re: zfs scrub enable by default Message-ID: <CAGuotKBmgYi9V-%2BO%2BOkjUqz_R_HGXYSQw%2BpaxSGOkLKoNnskpQ@mail.gmail.com> In-Reply-To: <F48A6A70-237E-4809-89DB-C7D12BE0FBFC@pk1048.com> References: <cca34d1a-1892-41ec-ce45-84865100c6e1@FreeBSD.org> <CAJjvXiEXEdAFXpXkGvt4fymA17kNdp6XkZV5taGKLoP2GvMHbw@mail.gmail.com> <d1b580da-1539-5fc9-f7a3-3f013bba4ef3@FreeBSD.org> <CANCZdfq2PneFvB4rnz2iGu5srFFFjs8N=7FwRO3DYjosESWXtQ@mail.gmail.com> <CAGuotKD0mCS3KmMA-EGL1uH_fByYOhMKbPVDoTdB8dg5kC-u9g@mail.gmail.com> <105090343.294898.1596586694925.JavaMail.zimbra@gray.id.au> <F48A6A70-237E-4809-89DB-C7D12BE0FBFC@pk1048.com>
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On Tue, Aug 4, 2020 at 11:36 PM PK1048.COM <info@pk1048.com> wrote: > > On Aug 4, 2020, at 8:18 PM, Grant Gray via freebsd-fs <freebsd-fs@freebsd= .org> wrote: > > > 2. That scrubbing PREVENTS data loss. Scrubbing can only tell you about= data loss AFTER it happens. Yes, it could alert you to a problem that prev= ents further data loss, but it's already too late. Scrubbing is not a subst= itute for RAID, backups and proactive SMART testing. > > Scrubbing does not directly prevent data loss. Scrubbing identifies data = returned from the underlying device as corrupt or incorrect. If the zpool h= as sufficient redundancy, then no data is lost. > > But, normal ZFS operation also identifies incorrect date returned from th= e underlying device(s). > > While I have only managed a few hundred drives under ZFS, I cannot recall= one case where a proactive scrub found bad data _before_ normal operations= . Once a checksum error is reported via `zpool status` then I have found a = scrub useful to determine the extent of the drive failure. > > I know there are others with thousands of drives managed under ZFS and th= eir experience may differ. > > In terms of whether the periodic scrub should be enabled by default, I am= undecided, as I can see both sides of the argument. I would prefer to make= it a user choice during installation as one of the ZFS options (such as na= tive 4K drives, ashift=3D12 or mirrored swap). Make the default enabled, bu= t by putting it in the installation options, those who know they need it di= sabled can make sure it is off from day one and not have a rude surprise th= e first time it runs (35 days after installation). > I don't think it was mentioned on this list, but that seems to be the current direction this is heading. Providing an option in the installer, whether enabled by default or not, should address everyone's concerns. --=20 Ryan Moeller iXsystems, Inc. OS Developer Email: ryan@iXsystems.com
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