From: Zdenek Kabelac <firstname.lastname@example.org> To: LVM general discussion and development <email@example.com>, Gionatan Danti <firstname.lastname@example.org> Cc: "Yu, Mingli" <Mingli.Yu@windriver.com> Subject: Re: [linux-lvm] The size specified by "lvcreate -L" is not accurate Date: Thu, 2 Sep 2021 16:23:34 +0200 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> Dne 02. 09. 21 v 15:24 Gionatan Danti napsal(a): > Il 2021-09-02 05:26 Yu, Mingli ha scritto: >> Per >> https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/tree/doc/RelNotes/v1.46.4.txt >> >> , after e2fsprogs upgrades to 1.46.4, the defaults for mke2fs now >> call for 256 byte inodes for all file systems (with the exception of >> file systems for the GNU Hurd, which only supports 128 byte inodes) >> and use "lvcreate -L 50 -n lv_test1 vg_test && mke2fs >> /dev/vg_test/lv_test1" and then continue to check the partiontion as >> below.(use lvm2 2.03.11 for the test) >> # df -h | grep dev/mapper/vg_test-lv_test1 >> >> /dev/mapper/vg_test-lv_test1 48M 14K 46M 1% /mnt/lv-test >> >> Though claim 50M as above, but it turns out to be only 48M. > > I think that allocation are done in multiple of physical extent size which, by > default, is at 4 MB. > 50 is not a multiple of 4 while 48 is, so "lvcreate" probably rounded down the > required size. > Using one or more "-v" should bring progressively more details. > Hi As correctly pointed out by Gionatan - lvm2 allocates LVs in 'extent_size' allocation units. So with default 4M - you could have either 48M or 52M. In your case - you likely get 52M (as that's how lvm2 behaves - you get at least specified amount of space rounded up to nearest extent - see output of 'lvs' command. However your formatted extX volume also does have some internal 'filesystem' metadata - so LV of size 52M gives reduced ext4 space to 48M in your case as most likely 'ext4' header size 'cuts' away possibly 4M alignment used by ext4. Anyway - you if you care about max usage of every single byte on your storage - you could further tune/lower lvm2 metadata size + alignment + extent_size and also same you could tuning you could try with ext4 settings. This way you could take back some wasted space on alignments - which normally is negligible amount of disk space on modern high capacity sized drives. Regards Zdenek _______________________________________________ linux-lvm mailing list email@example.com https://listman.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
prev parent reply other threads:[~2021-09-02 14:30 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-09-02 3:26 Yu, Mingli 2021-09-02 13:24 ` Gionatan Danti 2021-09-02 14:23 ` Zdenek Kabelac [this message]
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