From: "Theodore Ts'o" <tytso@mit.edu>
To: Thorsten Glaser <t.glaser@tarent.de>
Subject: Re: [PATCH 11/12] Add support for new compat feature "sparse_super2"
Date: Wed, 5 Feb 2014 11:17:11 -0500 [thread overview]
Message-ID: <20140205161711.GB11667@thunk.org> (raw)
In-Reply-To: <alpine.DEB.2.10.1402051559390.16807@tglase.lan.tarent.de>
On Wed, Feb 05, 2014 at 04:01:26PM +0100, Thorsten Glaser wrote:
>
> Can we have this for tune2fs? At least a way to turn it on, so that
> the next e2fsck or resize2fs will actually get rid of the now no
> longer needed copies?
Sure, it's possible. It's not like there are *that* many copies so it
won't actually save that much disk space. The main goal was not save
space, since the amount of disk space for the extra copies is a very
tiny fraction of the disk space in a big file system.
The main motivation for sparse superblocks was to allow me to make
file systems that are where the data block area is perfectly
contiguous which is useful for various specialized use cases. For
example, if you are a huge cloud company who is absolutely fanatical
about controlling 99.9 percentile latency, and you want to create data
block files which are completely contiguous. The sparse_super2
feature will also be useful for supporting Shingled Magnetic Recording
(SMR) disks where we care about having large, contiguous files be
aligned on 256 MB SMR zones, in the case where the userspace
application is SMR-aware. (SMR drives are only now starting to be
available in prototype form from HDD vendors, and the T10
specifications haven't been finalized yet, so these are still very
early days for SMR support.)
> What kernels support this option? (Sorry if this was already said…
> I mostly noticed this in today’s apt-listchanges output only, and
> DuckDuckGo found virtually nothing, and Google was only marginally
> more helpful.) Is this ext4fs only?
The sparse_super2 feature is a compat feature, so it doesn't have any
kernel dependencies, and no, it's not ext4 only. Any modern kernel
will have no problem supporting it. Some old 2.2 or 2.4 kernels with
ext3 might complain because blocks which they think should be reserved
for backup superblocks will not be, but that hasn't been true for
quite some time.
One restriction is that kernels currently do not support online resize
of sparse_super2 file systems. That will come eventually, but the
intended use case for this feature was primarily for single disk file
systems, so online resize wasn't something that is high on the
priority list.
Cheers,
- Ted
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next prev parent reply other threads:[~2014-02-06 12:19 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-20 5:54 [PATCH 00/12] e2fsprogs mke2fs optimizations and new features Theodore Ts'o
2014-01-20 5:54 ` [PATCH 01/12] libext2fs: fix off-by-one bug in ext2fs_extent_insert() Theodore Ts'o
2014-01-20 5:54 ` [PATCH 02/12] libext2fs: clean up generic handling of ext2fs_find_first_{set,zero}_*() Theodore Ts'o
2014-01-20 5:54 ` [PATCH 03/12] libext2fs: build tst_bitmaps with rep invariants checking enabled Theodore Ts'o
2014-01-20 5:54 ` [PATCH 04/12] libext: optimize find_first_set() for bitarray-based bitmaps Theodore Ts'o
2014-01-20 5:54 ` [PATCH 05/12] libext2fs: optimize find_first_{zero,set}() for red-black tree based bitmaps Theodore Ts'o
2014-01-20 5:54 ` [PATCH 06/12] libext2fs: further clean up and rename check_block_uninit Theodore Ts'o
2014-01-20 20:17 ` Darrick J. Wong
2014-01-20 5:54 ` [PATCH 07/12] libext2fs: add ext2fs_block_alloc_stats_range() Theodore Ts'o
2014-02-13 21:50 ` Darrick J. Wong
2014-01-20 5:54 ` [PATCH 08/12] libext2fs: optimize ext2fs_allocate_group_table() Theodore Ts'o
2014-01-20 5:54 ` [PATCH 09/12] libext2: optimize ext2fs_new_block2() Theodore Ts'o
2014-01-20 21:52 ` Andreas Dilger
2014-01-21 15:54 ` Theodore Ts'o
2014-01-20 5:54 ` [PATCH 10/12] mke2fs: optimize fix_cluster_bg_counts() Theodore Ts'o
2014-01-20 5:54 ` [PATCH 11/12] Add support for new compat feature "sparse_super2" Theodore Ts'o
2014-01-20 21:49 ` Andreas Dilger
[not found] ` <alpine.DEB.2.10.1402051559390.16807@tglase.lan.tarent.de>
2014-02-05 16:17 ` Theodore Ts'o [this message]
2014-01-20 5:54 ` [PATCH 12/12] mke2fs: allow metadata blocks to be at the beginning of the file system Theodore Ts'o
2014-01-20 16:30 ` Theodore Ts'o
2014-01-20 23:25 ` Andreas Dilger
2014-01-21 6:23 ` Theodore Ts'o
2014-01-23 21:28 ` Andreas Dilger
2014-01-20 16:30 ` [PATCH 00/12] e2fsprogs mke2fs optimizations and new features Theodore Ts'o
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