Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

ZFS: Apple's new filesystem that wasn't (2016)

ahl.dtrace.org

Post reply on HN
Print view View original

21–30 of 209 posts

Re: ZFS: Apple's new filesystem that wasn't (2016)

#21

Post by thfuran »

Dylan16807 wrote: post #17
jeroenhd wrote: post #11

I wonder what ZFS in the iPhone would've looked like. As far as I recall, the iPhone didn't have error correcting memory, and ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk. ZFS' RAM-hungry nature would've also forced Apple to add more memory to their phone.

> ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk I don't think it is. I've never heard of that happening, or seen any evidence ZFS is more likely to break than any random filesystem. I've only seen people spreading paranoid rumors based on a couple pages saying ECC memory is important to fully get the benefits of ZFS.

They also insist that you need about 10 TB RAM per TB disk space or something like that.

Re: ZFS: Apple's new filesystem that wasn't (2016)

#22

Post by smittywerben »

Thanks for sharing I was just looking for what happened to Sun. I like the second-hand quote comparing the IBM and HP as "garbage trucks colliding" plus the inclusion of blog posts with links to the court filings.

Is it fair to say ZFS made most sense on Solaris using Solaris Containers on SPARK?

Re: ZFS: Apple's new filesystem that wasn't (2016)

#23

Post by ahl »

nikhizzle wrote: post #18
rrdharan wrote: post #15

Kind of odd that the blog states that "The architect for ZFS at Apple had left" and links to the LinkedIn profile of someone who doesn't have any Apple work experience listed on their resume. I assume the author linked to the wrong profile?

Ex-Apple File System engineer here who shared an office with the other ZFS lead at the time. Can confirm they link to the wrong profile for Don Brady. This is the correct person: https://github.com/don-brady Also can confirm Don is one of the kindest, nicest principal engineer level people I’ve worked with in my career. Always had time to mentor and assist.

Not sure how I fat-fingered Don's LinkedIn, but I'm updating that 9-year-old typo. Agreed that Don is a delight. In the years after this article I got to collaborate more with him, but left Delphix before he joined to work on ZFS.

Re: ZFS: Apple's new filesystem that wasn't (2016)

#24

Post by terlisimo »

jeroenhd wrote: post #11

I wonder what ZFS in the iPhone would've looked like. As far as I recall, the iPhone didn't have error correcting memory, and ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk. ZFS' RAM-hungry nature would've also forced Apple to add more memory to their phone.

> ZFS is notorious for corrupting itself when bit flips

That is a notorious myth.

https://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-y...

Re: ZFS: Apple's new filesystem that wasn't (2016)

#26

Post by ahl »

jeroenhd wrote: post #11

I wonder what ZFS in the iPhone would've looked like. As far as I recall, the iPhone didn't have error correcting memory, and ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk. ZFS' RAM-hungry nature would've also forced Apple to add more memory to their phone.

It's very amusing that this kind of legend has persisted! ZFS is notorious for *noticing* when bits flip, something APFS designers claimed was rare given the robustness of Apple hardware.[1][2] What would ZFS on iPhone have looked like? Hard to know, and that certainly wasn't the design center.

Neither here nor there, but DTrace was ported to iPhone--it was shown to me in hushed tones in the back of an auditorium once...

[1]: https://arstechnica.com/gadgets/2016/06/a-zfs-developers-ana...

[2]: https://ahl.dtrace.org/2016/06/19/apfs-part5/#checksums

Re: ZFS: Apple's new filesystem that wasn't (2016)

#27

Post by zie »

mrkeen wrote: post #20
jeroenhd wrote: post #11

I wonder what ZFS in the iPhone would've looked like. As far as I recall, the iPhone didn't have error correcting memory, and ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk. ZFS' RAM-hungry nature would've also forced Apple to add more memory to their phone.

> ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk. What's a bit flip?

Basically it's that memory changes out from under you. As we know, computers use Binary, so everything boils down to it being a 0 or a 1. A bit flip is changing what was say a 0 into a 1.

Usually attributed to "cosmic rays", but really can happen for any number of less exciting sounding reasons.

Basically, there is zero double checking in your computer for almost everything except stuff that goes across the network. Memory and disks are not checked for correctness, basically ever on any machine anywhere. Many servers(but certainly not all) are the rare exception when it comes to memory safety. They usually have ECC(Error Correction Code) Memory, basically a checksum on the memory to ensure that if memory is corrupted, it's noticed and fixed.

Essentially every filesystem everywhere does zero data integrity checking:

  MacOS APFS: Nope
  Windows NTFS: Nope
  Linux EXT4: Nope
  BSD's UFS: Nope
  Your mobile phone: Nope
ZFS is the rare exception for file systems that actually double check the data you save to it is the data you get back from it. Every other filesystem is just a big ball of unknown data. You probably get back what you put it, but there is zero promises or guarantees.

Re: ZFS: Apple's new filesystem that wasn't (2016)

#28

Post by ahl »

mrkeen wrote: post #20
jeroenhd wrote: post #11

I wonder what ZFS in the iPhone would've looked like. As far as I recall, the iPhone didn't have error correcting memory, and ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk. ZFS' RAM-hungry nature would've also forced Apple to add more memory to their phone.

> ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk. What's a bit flip?

Sometimes data on disk and in memory are randomly corrupted. For a pretty amazing example, check out "bitsquatting"[1]--it's like domain name squatting, but instead of typos, you squat on domains that would bit looked up in the case of random bit flips. These can occur due e.g. to cosmic rays. On-disk, HDDs and SSDs can produce the wrong data. It's uncommon to see actual invalid data rather than have an IO fail on ECC, but it certainly can happen (e.g. due to firmware bugs).

[1]: https://en.wikipedia.org/wiki/Bitsquatting

Re: ZFS: Apple's new filesystem that wasn't (2016)

#29

Post by yjftsjthsd-h »

thfuran wrote: post #21
Dylan16807 wrote: post #17

Earlier quoted context omitted.

> ZFS is notorious for corrupting itself when bit flips hit it and break the checksum on disk I don't think it is. I've never heard of that happening, or seen any evidence ZFS is more likely to break than any random filesystem. I've only seen people spreading paranoid rumors based on a couple pages saying ECC memory is important to fully get the benefits of ZFS.

They also insist that you need about 10 TB RAM per TB disk space or something like that.

There is a rule of thumb that you should have at least 1 GB of RAM per TB of disk when using deduplication. That's.... Different.

Re: ZFS: Apple's new filesystem that wasn't (2016)

#30

Post by ahl »

Back in 2016, Ars Technica picked up this piece from my blog [1] as well as a longer piece reviewing the newly announced APFS [2] [3]. Glad it's still finding an audience!

[1]: https://arstechnica.com/gadgets/2016/06/zfs-the-other-new-ap...

[2]: https://ahl.dtrace.org/2016/06/19/apfs-part1/

[3]: https://arstechnica.com/gadgets/2016/06/a-zfs-developers-ana...

Post reply on HN