From: Edward Shishkin <firstname.lastname@example.org> To: Chris Mason <email@example.com>, Edward Shishkin <firstname.lastname@example.org>, Mat <email@example.com>, LKML <firstname.lastname@example.org>, email@example.com, Ric Subject: Re: Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs) Date: Fri, 18 Jun 2010 18:22:39 +0200 Message-ID: <4C1B9D4F.firstname.lastname@example.org> (raw) In-Reply-To: <20100618151017.GN27466@think> Chris Mason wrote: > On Fri, Jun 18, 2010 at 05:05:46PM +0200, Edward Shishkin wrote: > >> Chris Mason wrote: >> >>> On Fri, Jun 18, 2010 at 03:32:16PM +0200, Edward Shishkin wrote: >>> >>>> Mat wrote: >>>> >>>>> On Thu, Jun 3, 2010 at 4:58 PM, Edward Shishkin <email@example.com> wrote: >>>>> >>>>>> Hello everyone. >>>>>> >>>>>> I was asked to review/evaluate Btrfs for using in enterprise >>>>>> systems and the below are my first impressions (linux-2.6.33). >>>>>> >>>>>> The first test I have made was filling an empty 659M (/dev/sdb2) >>>>>> btrfs partition (mounted to /mnt) with 2K files: >>>>>> >>>>>> # for i in $(seq 1000000); \ >>>>>> do dd if=/dev/zero of=/mnt/file_$i bs=2048 count=1; done >>>>>> (terminated after getting "No space left on device" reports). >>>>>> >>>>>> # ls /mnt | wc -l >>>>>> 59480 >>>>>> >>>>>> So, I got the "dirty" utilization 59480*2048 / (659*1024*1024) = 0.17, >>>>>> and the first obvious question is "hey, where are other 83% of my >>>>>> disk space???" I looked at the btrfs storage tree (fs_tree) and was >>>>>> shocked with the situation on the leaf level. The Appendix B shows >>>>>> 5 adjacent btrfs leafs, which have the same parent. >>>>>> >>>>>> For example, look at the leaf 29425664: "items 1 free space 3892" >>>>>> (of 4096!!). Note, that this "free" space (3892) is _dead_: any >>>>>> attempts to write to the file system will result in "No space left >>>>>> on device". >>>>>> >>> There are two easy ways to fix this problem. Turn off the inline >>> extents (max_inline=0) or allow splitting of the inline extents. I >>> didn't put in the splitting simply because the complexity was high while >>> the benefits were low (in comparison with just turning off the inline >>> extents). >>> >> Hello, Chris. Thanks for response! >> I afraid that both ways won't fix the problem. Look at this leaf: >> >> [...] >> leaf 29425664 items 1 free space 3892 generation 8 owner 5 >> fs uuid 50268d9d-2a53-4f4d-b3a3-4fbff74dd956 >> chunk uuid 963ba49a-bb2b-48a3-9b35-520d857aade6 >> item 0 key (320 XATTR_ITEM 3817753667) itemoff 3917 itemsize 78 >> location key (0 UNKNOWN 0) type 8 >> namelen 16 datalen 32 name: security.selinux >> [...] >> >> There is no inline extents, and what are you going to split here? >> All leafs must be at least a half filled, otherwise we loose all >> boundaries, which provides non-zero utilization.. >> > > Right, there is no inline extent because we require them to fit entirely > in the leaf. So we end up with mostly empty leaves because the inline > item is large enough to make it difficult to push around but not large > enough to fill the leaf. > How about left and right neighbors? They contain a lot of free space (1572 and 1901 respectively). I am not happy with the very fact of such shallow leafs which contain only one small (xattr) item..
next prev parent reply index Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-06-03 14:58 Unbound(?) internal fragmentation in Btrfs Edward Shishkin [not found] ` <AANLkTilKw2onQkdNlZjg7WVnPu2dsNpDSvoxrO_FA2z_@mail.gmail.com> 2010-06-18 8:03 ` Christian Stroetmann 2010-06-18 13:32 ` Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs) Edward Shishkin 2010-06-18 13:45 ` Daniel J Blueman 2010-06-18 16:50 ` Edward Shishkin 2010-06-23 23:40 ` Jamie Lokier 2010-06-24 3:43 ` Daniel Taylor 2010-06-24 4:51 ` Mike Fedyk 2010-06-24 22:06 ` Daniel Taylor 2010-06-25 9:15 ` Btrfs: broken file system design Andi Kleen 2010-06-25 18:58 ` Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs) Ric Wheeler 2010-06-26 5:18 ` Michael Tokarev 2010-06-26 11:55 ` Ric Wheeler [not found] ` <57784.2001:5c0:82dc::firstname.lastname@example.org> 2010-06-26 13:47 ` Ric Wheeler 2010-06-24 9:50 ` David Woodhouse 2010-06-18 18:15 ` Christian Stroetmann 2010-06-18 13:47 ` Chris Mason 2010-06-18 15:05 ` Edward Shishkin [not found] ` <4C1B8B4A.email@example.com> 2010-06-18 15:10 ` Chris Mason 2010-06-18 16:22 ` Edward Shishkin [this message] [not found] ` <4C1B9D4F.firstname.lastname@example.org> 2010-06-18 18:10 ` Chris Mason 2010-06-18 15:21 ` Christian Stroetmann 2010-06-18 15:22 ` Chris Mason 2010-06-18 15:56 ` Jamie Lokier 2010-06-18 19:25 ` Christian Stroetmann 2010-06-18 19:29 ` Edward Shishkin 2010-06-18 19:35 ` Chris Mason 2010-06-18 22:04 ` Balancing leaves when walking from top to down (was Btrfs:...) Edward Shishkin [not found] ` <4C1BED56.email@example.com> 2010-06-18 22:16 ` Ric Wheeler 2010-06-19 0:03 ` Edward Shishkin 2010-06-21 13:15 ` Chris Mason [not found] ` <20100621180013.GD17979@think> 2010-06-22 14:12 ` Edward Shishkin 2010-06-22 14:20 ` Chris Mason 2010-06-23 13:46 ` Edward Shishkin [not found] ` <4C221049.firstname.lastname@example.org> 2010-06-23 23:37 ` Jamie Lokier 2010-06-24 13:06 ` Chris Mason 2010-06-30 20:05 ` Edward Shishkin [not found] ` <4C2BA381.email@example.com> 2010-06-30 21:12 ` Chris Mason 2010-07-09 4:16 ` Chris Samuel 2010-07-09 20:30 ` Chris Mason 2010-06-23 23:57 ` Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs) Jamie Lokier
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