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Silent Data Corruption Is Real

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Re: Silent Data Corruption Is Real

#51
post #47
post #37

Earlier quoted context omitted.

I think he means portability of the software. What I want to 'ZFS import' on a Windows or macOS machine?

Oh, well it's ported from Solaris to illumos and FreeBSD and to a lesser extent OS X and Linux. So I'm still confused about the portability claim.

The license incompatibility has kept it out of the mainline kernel for Linux, so it's not really a viable option there in many situations. Linux is definitely lacking in this department.

Re: Silent Data Corruption Is Real

#52
post #6

Earlier quoted context omitted.

Btrfs has experienced some data loss bugs in recent memory. It looks like ZFS is the only remaining option. https://www.phoronix.com/scan.php?page=news_item&px=Btrfs-Da... https://www.spinics.net/lists/linux-btrfs/msg59190.html https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg...

Any idea if ZFS plays well with Ubuntu's full-disk encryption? I've used the FDE option at install for years and every time I upgrade (I wipe & reinstall every year or so) I try to understand how to first set up ZFS, then FDE, and then I realize it's far too complicated for me. Any good tutorials or setup guides that even a moron could understand? I've got a pretty good setup now with a fairly complex fstab, multiple…

I use it all over with LUKS on Ubuntu. It works fine, but there's one little hitch:

when calling anything that ultimately calls grub-probe (e.g. apt-get upgrade), you have to symlink the decrypted device mapper volume up a layer into /dev because grub-probe can't seem to find the ZFS vdev(s) otherwise. ie: "ln -s /dev/mapper/encrypted-zfs-vdev /dev".

This is in fact the case on every Linux distribution I've run ZFS over dm-crypt on.

EDIT: IOW its a grub bug not an Ubuntu bug.

Re: Silent Data Corruption Is Real

#53
post #38

Earlier quoted context omitted.

You could use ZFS, then the file cannot silently become corrupted.

Yes it can. ZFS will only notice next time you scrub or read the sector.

Sure, but your ZFS pool will have redundancy, and ZFS will know which block was corrupted. This lets it recover from the error.

Re: Silent Data Corruption Is Real

#54
post #6

Earlier quoted context omitted.

Btrfs has experienced some data loss bugs in recent memory. It looks like ZFS is the only remaining option. https://www.phoronix.com/scan.php?page=news_item&px=Btrfs-Da... https://www.spinics.net/lists/linux-btrfs/msg59190.html https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg...

Any idea if ZFS plays well with Ubuntu's full-disk encryption? I've used the FDE option at install for years and every time I upgrade (I wipe & reinstall every year or so) I try to understand how to first set up ZFS, then FDE, and then I realize it's far too complicated for me. Any good tutorials or setup guides that even a moron could understand? I've got a pretty good setup now with a fairly complex fstab, multiple…

Native ZFS encryption may become available soon. It is pending code review: https://github.com/zfsonlinux/zfs/pull/5769

There was a presentation of this by Tom Caputi at the most recent OpenZFS Developer Summit.

Slides: https://drive.google.com/file/d/0B5hUzsxe4cdmU3ZTRXNxa2JIaDQ... Video: https://youtu.be/frnLiXclAMo Conference: http://open-zfs.org/wiki/OpenZFS_Developer_Summit

Re: Silent Data Corruption Is Real

#55
post #48

Earlier quoted context omitted.

ZFS on OSX has been revived I believe.

I wonder if the recent Linux syscall emulation on Windows would somehow make it possible or easier to port ZFS on Linux to Windows. I know you have the SPL anyway, so maybe with the addition of the Linux POSIX-ish layer in there this could be the case...

Short answer: No it wouldn't make it easier to port.

Longer answer: The Linux subsystem in Windows 10 only deals with userspace. It doesn't support kernel modules nor changes anything about making Windows drivers. Porting ZFS to Windows is certainly possible, but it will take quite a lot of effort, and the Linux subsystem is irrelevant in that situation.

Re: Silent Data Corruption Is Real

#56
post #55
post #48

Earlier quoted context omitted.

I wonder if the recent Linux syscall emulation on Windows would somehow make it possible or easier to port ZFS on Linux to Windows. I know you have the SPL anyway, so maybe with the addition of the Linux POSIX-ish layer in there this could be the case...

Short answer: No it wouldn't make it easier to port. Longer answer: The Linux subsystem in Windows 10 only deals with userspace. It doesn't support kernel modules nor changes anything about making Windows drivers. Porting ZFS to Windows is certainly possible, but it will take quite a lot of effort, and the Linux subsystem is irrelevant in that situation.

Yeah, I figured as much, but was hoping there might be something about the Linux subsystem that would be helpful in porting drivers around, beyond userspace.

Obviously, I've yet to actually use it myself.

Re: Silent Data Corruption Is Real

#57
post #23
post #3

It really bugs me (and has for a while) that there is still no mainstream linux filesystem that supports data block checksumming. Silent corruption is not exactly new, and the odds of running into it have grown significantly as drives have gotten bigger. It's a bit maddening that nobody seems to care (or maybe I'm just looking in the wrong places) (...sure, you could call zfs or btrfs "mainstream", I suppose, but whe…

btrfs only uses CRC32c which is weakish. ZFS is great but not exactly portable. I started to use Borg now for archiving purposes as well, not just backup. For me (low access concurrency, i.e. single or at most "a few" users) that works very well. Portable + strong checksumming + strong crypto + mountable + reasonable speed (with prospect of more) is a good package. It doesn't solve error correction, though.

Not portable? In comparison to which filesytems? I can easily export a ZFS pool on Linux, physically transport the discs to a FreeBSD or IllumOS server and import the pool. Or to MacOS X, which is also supported (though I haven't tried it unlike the others where it worked perfectly).

That's already far ahead of ext, ufs, xfs, jfs, btrfs etc. The only ones offhand which are possibly more portable are fat, hfs, udf and ntfs, and you're not exactly going to want to use them for any serious purpose on a Unix system. ZFS is the most portable and featureful Unix filesystem around at present IMHO.

Re: Silent Data Corruption Is Real

#58

Shouldn't RAID 1,5,6 protect against data corruption because of disk errors?

Some disk errors, yes, but something as simple as a power failure can easily corrupt your data: http://www.raid-recovery-guide.com/raid5-write-hole.aspx https://blogs.oracle.com/bonwick/entry/raid_z

Hardware RAID does not suffer from the write-hole like MD-RAID does (thanks to on-board supercap-backed non-volatile memory).

I can't remember if it was merged upstream, but some folks from Facebook worked on a write-back cache for MD-RAID (4/5/6 personalities) in Linux which essentially closes the write-hole too. It allows one to stage dirty RAID stripe data in a non-volatile medium (NVDIMMs/flash) before submitting block requests to the underlying array. On recovery, the cache is scanned for dirty stripes, which are restored before actually using the P/Q parity to rebuild user data. I worked on something similar in a prior project where we cached dirty stripes in an NVDIMM, and also mirrored it on its controller-pair (in a dual-controller server architecture) using NTB. It was a fun project, when neither the PMEM nor the NTB driver subsystems were in the mainline kernel.

Re: Silent Data Corruption Is Real

#59
I started a really simple and effective project the last month to be able to fix from bitrot in linux(MacOs/Unix?). It's "almost done" just need more real testing and make the systemd service. I've been pretty busy the last weeks so I've only been able to improve the bitrot performance.

https://github.com/liloman/heal-bitrots

Unfortunatly, btrfs is not stable and zfs needs a "super computer" or at least as much GBs of ECC RAM as you can buy. This solution is designed to any machine and any FS.

Re: Silent Data Corruption Is Real

#60
post #51
post #47

Earlier quoted context omitted.

Oh, well it's ported from Solaris to illumos and FreeBSD and to a lesser extent OS X and Linux. So I'm still confused about the portability claim.

The license incompatibility has kept it out of the mainline kernel for Linux, so it's not really a viable option there in many situations. Linux is definitely lacking in this department.

That's a minor concern and unrelated to the portability claim. That comes down to choice, and is not a technical consideration. I'm using it with Ubuntu 16.04 LTS and 16.10 where it works out of the box. It's most certainly portable to and from Linux and other systems; I've done it personally, and it works a treat.
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