[lustre-discuss] size of MDT, inode count, inode size

[Thomas Roth]

Hmm, option-testing leads to more confusion:

With this 922GB-sdb1 I do

mkfs.lustre --reformat --mgs --mdt ... /dev/sdb1

The output of the command says

    Permanent disk data:
Target:     test0:MDT0000
...

device size = 944137MB
formatting backing filesystem ldiskfs on /dev/sdb1
	target name   test0:MDT0000
	4k blocks     241699072
	options        -J size=4096 -I 1024 -i 2560 -q -O 
dirdata,uninit_bg,^extents,mmp,dir_nlink,quota,huge_file,flex_bg -E lazy_journal_init -F

mkfs_cmd = mke2fs -j -b 4096 -L test0:MDT0000  -J size=4096 -I 1024 -i 2560 -q -O 
dirdata,uninit_bg,^extents,mmp,dir_nlink,quota,huge_file,flex_bg -E lazy_journal_init -F /dev/sdb1 
241699072


Mount this as ldiskfs, gives 369 M inodes.

One would assume that specifying one / some of the mke2fs-options here in the mkfs.lustre-command will 
change nothing.
However,

mkfs.lustre --reformat --mgs --mdt ... --mkfsoptions="-I 1024" /dev/sdb1

says

device size = 944137MB
formatting backing filesystem ldiskfs on /dev/sdb1
	target name   test0:MDT0000
	4k blocks     241699072
	options       -I 1024 -J size=4096 -i 1536 -q -O 
dirdata,uninit_bg,^extents,mmp,dir_nlink,quota,huge_file,flex_bg -E lazy_journal_init -F

mkfs_cmd = mke2fs -j -b 4096 -L test0:MDT0000 -I 1024 -J size=4096 -i 1536 -q -O 
dirdata,uninit_bg,^extents,mmp,dir_nlink,quota,huge_file,flex_bg -E lazy_journal_init -F /dev/sdb1 
241699072

and the mounted devices now has 615 M inodes.

So, whatever makes the calculation for the "-i / bytes-per-inode" value becomes ineffective if I 
specify the inode size by hand?

How many bytes-per-inode do I need?

This ratio, is it what the manual specifies as "one
inode created for each 2kB of LUN" ?

Perhaps the raw size of an MDT device should better be such that it leads to "-I 1024 -i 2048"?


Regards,
Thomas

On 01/26/2018 03:10 PM, Thomas Roth wrote:
> Hi all,
> 
> what is the relation between raw device size and size of a formatted MDT? Size of inodes + free space 
> = raw size?
> 
> The example:
> 
> MDT device has 922 GB in /proc/partions.
> Formatted under Lustre 2.5.3 with default values for mkfs.lustre resulted in a 'df -h' MDT of 692G and 
> more importantly 462M inodes.
> 
> So, the space used for inodes + the 'df -h' output add up to the raw size:
>   462M inodes * 0.5kB/inode + 692 GB = 922 GB
> 
> On that system there are now 330M files, more than 70% of the available inodes.
> 'df -h' says '692G  191G  456G  30% /srv/mds0'
> 
> What do I need the remaining 450G for? (Or the ~400G left once all the inodes are eaten?)
> Should the format command not be tuned towards more inodes?
> 
> 
> 
> Btw, on a Lustre 2.10.2 MDT I get 369M inodes and 550 G space (with a 922G raw device): inode size is 
> now 1024.
> However, according to the manual and various Jira/Ludocs the size should be 2k nowadays?
> 
> 
> Actually, the command within mkfs.lustre reads
> mke2fs -j -b 4096 -L test0:MDT0000  -J size=4096 -I 1024 -i 2560  -F /dev/sdb 241699072
> 
> -i 2560 ?
> 
> 
> Cheers,
> Thomas
> 
> 
> 

-