Date:	Sat, 16 Sep 2006 17:56:02 +0300
From:	"Pavel Mironchik" <tibor0@...il.com>
To:	"Theodore Tso" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: ext2/3 create large filesystem takes too much time; solutions

Hi Ted,

Thanks for the responce...
I agree with you and I would prefer to send something more
serious on that list than those previous patches - I like your
idea with counters. Btw I assume crc is more preferable than
just control sum for block group descriptors....

Pavel
p.mironchik@...esys.com
tibor@...linux.org

On 9/16/06, Theodore Tso <tytso@....edu> wrote:
> On Tue, Sep 12, 2006 at 02:07:34PM +0300, Pavel Mironchik wrote:
> >
> > Ext2/3 does erase of inode tables, when do creation of new systems.
> > This is very very long operation when the target file system volume is more
> > than
> > 2Tb. Other filesystem are not affected by such huge delay on creation of
> > filesystem. My concern was to improve design of ext3 to decrease time
> > consuption of creation large ext3 volumes on storage servers.
> > In general to solve problem, we should defer job of cleaning nodes to
> > kernel. In e2fsprogs there is LAZY_BG options but it  just avoids doing
> > erase of inodes only.
>
> Hi Pavel,
>
>         Apologies that no one responded right away; I think a lot of
> people have been incredibly busy.  I've been doing a huge amount of
> travel myself personally, and so my e-mail latency has been larger
> than normal.
>
>         The problem of long mke2fs problems is one that we've
> considered, and we do want to do something with it, but it's not been
> as high priority as some of the other problems on our hit list.
> Certainly, given that inode space is very precious, I'm not convinced
> that breaking backwards compatibility and burning an extra 16 bytes
> per inode is worth the net gain --- although there are other solutions
> that don't have that particular cost.  Yes, they take more lines of
> code to support, but given the hopefully large number of people that
> will be using ext4, I'd must rather spend an extra amount of
> development time getting it right, than doing something fast and dirty
> which then everyone pays for, over and over, again and again and again
> across millions and millions of machines!
>
>
> > I see several solutions for that problem:
> > 1) Add special bitmaps into fs header (inode groups descriptors?).
> > By looking at those bitmaps kernel could determine if inode is not cleaned,
> > and that inode will be propertly initialized.
>
> Actually, you don't need a bitmap; a much simpler solution is to have
> an integer field in the block group descriptors which indicates the
> number of inods that have been initialized in that block group.  The
> problem though is that what if the block group descriptors (or the
> bitmaps) get corrupted?  So what we also want to do is to add support
> for checksums in the individual inodes and in the block group
> descriptors themselves, as a double-check.
>
> These are useful features in and of themselves, and there are some
> sample implementations of them (for example, in the Iron ext2 paper).
> So my thinking is that we should get that work into ext4, and then
> it's not hard to add the support for fields in the block group
> descriptors that would allow for fast mke2fs support.
>
> Regards,
>
>                                                 - Ted
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