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Date: Wed, 8 Jun 2011 18:33:21 +0300 From: "Amir G." <amir73il@...rs.sourceforge.net> To: Eric Sandeen <sandeen@...hat.com> Cc: Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org, tytso@....edu, linux-kernel@...r.kernel.org Subject: Re: [PATCH v1 00/30] Ext4 snapshots On Wed, Jun 8, 2011 at 6:22 PM, Eric Sandeen <sandeen@...hat.com> wrote: > On 6/8/11 10:01 AM, Amir G. wrote: >> On Wed, Jun 8, 2011 at 5:41 PM, Eric Sandeen <sandeen@...hat.com> wrote: >>> On 6/8/11 9:04 AM, Amir G. wrote: >>>>> And one last note, I also think that the snapshot format change in the >>>>>> future, when we'll have snpashots with 64bit feature compatible seems >>>>>> just wrong to me. Adding some features or changing the implementation a >>>>>> bit is ok, but format change is different. When the code is upstream and >>>>>> stable it is just wrong. >>>> What can I say, I understand why it looks bad, but is 64bit code >>>> upstream and stable? Hell no! e2fsprogs 64bit is not out yet! >>>> There is no reason to call it 'format change'. >>>> It's going to be a new format used only for 64bit fs, which are not >>>> even out there yet. And when they are finally out there, they won't >>>> have >>>> snapshots until the new format is implemented. >>> >>> Well, the on-disk format for 64-bit (48-bit?) ext4 is there & fixed; it's >>> just that there is no released userspace which can properly handle it, right? >> >> I don't know, you tell me. >> Are there many users out there using 64bit feature, without the proper >> user space tools? > > No, but that doesn't mean the disk format has to change when the tools > come out... I just don't want to confuse "there are no tools" with > "the disk format is unstable" - Andreas et. al. have been using > that format for years. > >>> >>> I don't anticipate ext4 format changes for >16T, or am I missing something? >>> >>> -Eric >>> >> >> Argh! I wish I hadn't missed the Monday call (it's >> not in a good time for me). >> This whole 'format change' has gone out of control >> and I find it hard to present my case properly on scattered emails. > > Sorry; I may have just misunderstood... > >> The message I am trying to get through is: >> There is 32bit snapshot file format, which is implemented and well tested. >> There is 64bit snapshot file format, which is not implemented yet, so >> 64bit and snapshot feature are mutually exclusive. >> If and when 64bit snapshot file format will be implemented, it will be >> a new type of extent mapped file (v2) with 48bit logical addresses. >> Is this a 'format change'? Call it what you will, but it shouldn't >> affect anything on existing structures. It should only affect the >> non-existing structure of 64bit snapshot file. >> >> Does this answer your question? > > Yes, I guess I had misunderstood your point; I thought you were > implying that ext4's format had to change to support 64-bit, so why > not change snapshots along with it.... > > But you're just saying that you wish to push 32-bit snapshots which only > work with certain sizes of ext4 filesystems now, and later you will > release a new snapshot format which works with the larger filesystems. > Right? Right. Where 'Larger filesystems' := 64bit block addresses. > > (I don't actually know if we'll ever have 64-bit ext4, though, there > are still so many scaling issues beyond just being able to mkfs, > mount, growfs etc ... it's a serious game of catch-up with xfs > in that space, IMHO, which has been doing it well for years now...) More of a good reason to push a snapshot file format that work well with 32bit ext4. > > Still, pushing snapshots upstream which will have an on-disk format > more limited than the rest of the filesystem's on-disk format > does strike me as suboptimal from a pure technical design POV. > > What if we proposed, say, xattr code that could only apply xattrs > to files located in the first 16T? I don't think it'd be accepted. That is not a correct analogy. The correct analogy is not supporting xattrs on 64-bit ext4. Whether it makes sense or not for snapshots depends IMHO on whether people find snapshot on 32bit ext4 only useful or not. I naturally think that people will find it useful. Anyone can add snapshots to his existing 32-bit ext4, No one can migrate the same fs to 64-bit... > > I understand that you have a history and a format and a business case, > but that really should not change whether we do it right the first time, > upstream, IMHO... But I'm just the peanut gallery, here.... ;) > > -Eric > >> Amir. >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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