Date: Tue, 30 Apr 2019 10:41:17 +1000 From: Michelle Sullivan <michelle@sorbs.net> To: Alan Somers <asomers@freebsd.org> Cc: freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: ZFS... Message-ID: <56833732-2945-4BD3-95A6-7AF55AB87674@sorbs.net> In-Reply-To: <CAOtMX2gf3AZr1-QOX_6yYQoqE-H%2B8MjOWc=eK1tcwt5M3dCzdw@mail.gmail.com> References: <30506b3d-64fb-b327-94ae-d9da522f3a48@sorbs.net> <CAOtMX2gf3AZr1-QOX_6yYQoqE-H%2B8MjOWc=eK1tcwt5M3dCzdw@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Comments inline.. Michelle Sullivan http://www.mhix.org/ Sent from my iPad > On 30 Apr 2019, at 03:06, Alan Somers <asomers@freebsd.org> wrote: >=20 >> On Mon, Apr 29, 2019 at 10:23 AM Michelle Sullivan <michelle@sorbs.net> w= rote: >>=20 >> I know I'm not going to be popular for this, but I'll just drop it here >> anyhow. >>=20 >> http://www.michellesullivan.org/blog/1726 >>=20 >> Perhaps one should reconsider either: >>=20 >> 1. Looking at tools that may be able to recover corrupt ZFS metadata, or >> 2. Defaulting to non ZFS filesystems on install. >>=20 >> -- >> Michelle Sullivan >> http://www.mhix.org/ >=20 > Wow, losing multiple TB sucks for anybody. I'm sorry for your loss. > But I want to respond to a few points from the blog post. >=20 > 1) When ZFS says that "the data is always correct and there's no need > for fsck", they mean metadata as well as data. The spacemap is > protected in exactly the same way as all other data and metadata. (to > be pedantically correct, the labels and uberblocks are protected in a > different way, but still protected). The only way to get metadata > corruption is due a disk failure (3-disk failure when using RAIDZ2), > or due to a software bug. Sadly, those do happen, and they're > devilishly tricky to track down. The difference between ZFS and older > filesystems is that older filesystems experience corruption during > power loss _by_design_, not merely due to software bugs. A perfectly > functioning UFS implementation will experience corruption during power > loss, and that's why it needs to be fscked. It's not just > theoretical, either. I use UFS on my development VMs, and they > frequently experience corruption after a panic (which happens all the > time because I'm working on kernel code). I know, which is why I have ZVOLs with UFS filesystems in them for the devel= opment VMs... in a perfect world the power would have been all good, the up= ses would not be damaged and the generator would not run out of fuel because= of extended outage... in fact if it was a perfect world I wouldn=E2=80=99t= have my own mini dc at home. >=20 > 2) Backups are essential with any filesystem, not just ZFS. After > all, no amount of RAID will protect you from an accidental "rm -rf /". You only do it once... I did it back in 1995... haven=E2=80=99t ever done i= t again. >=20 > 3) ZFS hotspares can be swapped in automatically, though they don't be > default. It sounds like you already figured out how to assign a spare > to the pool. To use it automatically, you must set the "autoreplace" > pool property and enable zfsd. The latter can be done with "sysrc > zfsd_enable=3D"YES"". The system was originally built on 9.0, and got upgraded through out the yea= rs... zfsd was not available back then. So get your point, but maybe you di= dn=E2=80=99t realize this blog was a history of 8+ years? >=20 > 4) It sounds like you're having a lot of power trouble. Have you > tried sysutils/apcupsd from ports? I did... Malta was notorious for it. Hence 6kva upses in the bottom of each= rack (4 racks), cross connected with the rack next to it and a backup gener= ator... Australia on the otherhand is a lot more stable (at least where I a= m)... 2 power issues in 2 years... both within 10 hours... one was a transf= ormer, the other when some idiot took out a power pole (and I mean actually t= ook it out, it was literally snapped in half... how they got out of the car a= nd did a runner before the police or Ambos got there I=E2=80=99ll never know= .) > It's fairly handy. It can talk to > a wide range of UPSes, and can be configured to do stuff like send you > an email on power loss, and power down the server if the battery gets > too low. >=20 They could help this... all 4 upses are toast now. One caught fire, one no l= onger detects AC input, the other two I=E2=80=99m not even trying after the f= irst catching fire... the lot are being replaced on insurance. It=E2=80=99s a catalog of errors that most wouldn=E2=80=99t normally experie= nce. However it does show (to me) that ZFS on everything is a really bad id= ea... particularly for home users where there is unknown hardware and you kn= ow they will mistreat it... they certainly won=E2=80=99t have ECC RAM in lap= tops etc... unknown caching facilities etc.. it=E2=80=99s a recipe for losin= g the root drive... Regards, Michelle=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?56833732-2945-4BD3-95A6-7AF55AB87674>