From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3780FF87.2C90F77D@moeraki.com> Date: Mon, 05 Jul 1999 11:55:03 -0700 From: John Finlay MIME-Version: 1.0 Subject: Re: [linux-lvm] Re: ext2resize References: <010e01bec6c3$06ebed80$0102010a@adminstation.sgymsdam.nl> Content-Transfer-Encoding: 7bit Sender: owner-linux-lvm Errors-To: owner-linux-lvm List-Id: Content-Type: text/plain; charset="us-ascii" To: Lennert Buytenhek Cc: linux-lvm@msede.com Lennert Buytenhek wrote: > >Lennert Buytenhek writes: > >> I replied: "Depending on who you talk to of course. :-) The max. number > >> of groups for ext2 is 1024 I believe. One extra gd block per block gives > >> you room for 32*8=256mb expansion (assuming 1kb blocks). This > >> will cost you at most 1 meg of reserved gd blocks. Seems like a fair > >> price. The max. number of gd blocks is 32. So doing this when making > >> an fs will cost you at most 32*1024 blocks, which is 32mb with 1k > >> blocks. On modern drives, you'll probably not even notice a 32mb > >> loss. Unless you have a lot of partitions, of course...." > >Are you sure that the max number of GDT blocks is 32? For a 1kB block > > Yes, for a 1kb block size. One of my ext2 linux kernel headers #defines > the max number of groups to be 1024. Times 32 bytes per group > descriptor is 32kb, which is 32 blocks on 1kb. Unless the header is > wrong, of course. > I don't think this is correct. I have an ext2 filesystem that is 52GB. It appears to have 200+ blocks in the GDT and as I recall 6000+ block groups. I made a 86GB filesystem the other day with 1k blocks and it had 10000+ block groups. With 4k blocks there were 650+ block groups. > > >size, this would give a limit of 32 GDT blocks * 32 GD/GDT block * 8k > >blocks/GD = 8GB max FS size. With 4kB blocks we grow 4x for larger data > >blocks, 4x for more GD/GDT block, and 4x for more blocks/GD, so 512 GB > >max, not the expected 4TB limit. If we wanted to reach 4TB with 1kB > >blocks (possible since block numbers are 32-bit unsigned), then we would > >need 512*32 GDT blocks, or 200% !!! of all FS space, while with 4kB > >blocks we need 256 GDT blocks, or 1/32 of FS space. > > Yes, well, I didn't invent this. Most of the people will use larger block > sizes then, anyway. > It does seem peculiar that the largest block size is limited to 4k. 8k would seem to be a reasonable size to me. It seems that ext2 is not really suited for large filesystems: seems like there is too much redundancy in the block groups that causes slow downs in operations like mount, etc.; e2fsck takes hours on a 52GB filesystem. Are there any projects underway to develop a new filesystem that is more suitable for large filesystems? John