Ytdyklly

I would be formatting a newish large capacity 4 TB hdd in few hours. From what little I understand, I could just format it and it will look to be formatted.

If I format it in real-time then it would probably take a long time, 10000 rpm x 4 GB DDR3 RAM. Hence Linux came up with the concept of ext4lazyinit.

I'm running Debian GNU/Linux 'Stretch' and have kernel 4.9 .

[$] uname -a



Linux debian 4.9.0-1-amd64 #1 SMP Debian 4.9.2-2 (2017-01-12) x86_64 GNU/Linux



[$] lsb_release -a



No LSB modules are available.

Distributor ID: Debian

Description:    Debian GNU/Linux 9.0 (stretch)

Release:    9.0

Codename:   stretch    

Now, according to the wiki it says and I quote -

If enabled and the uninit_bg feature is enabled, the inode table will
not be fully initialized by mke2fs. This speeds up file system
initialization noticeably, but it requires the kernel to finish
initializing the file system in the background when the file system is
first mounted. If the option value is omitted, it defaults to 1 to
enable lazy inode table zeroing. - Thomas Kenn

Now is there a way to know if the above feature is enabled in my kernel or not ?

Update -

there is a /boot/config-4.9.0-1-amd64 . The file is 7865 lines long according to -

[$] cat /boot/config-4.9.0-1-amd64 | tail -n 1



  7865  CONFIG_SBITMAP=y

Trying to grep doesn't lead anywhere -

[$] cat /boot/config-4.9.0-1-amd64 | grep LAZY

OR even ext4 for that manner -

[$] cat /boot/config-4.9.0-1-amd64 | grep EXT4



  6895  CONFIG_EXT4_FS=m

  6896  CONFIG_EXT4_USE_FOR_EXT2=y

  6897  CONFIG_EXT4_FS_POSIX_ACL=y

  6898  CONFIG_EXT4_FS_SECURITY=y

  6899  CONFIG_EXT4_ENCRYPTION=y

  6900  CONFIG_EXT4_FS_ENCRYPTION=y

  6901  # CONFIG_EXT4_DEBUG is not set

Any ideas anybody ?

Google for its kernel compilation string (or check this in the "make menuconfig" of the kernel source). It surely starts with CONFIG_EXT4_FS_ . These kernel compilation flags of your actually running kernel are can be provided in /proc/config.gz (but doing this is also a kernel compile flag, thus it may or may not be enabled on your system), or by your distribution in /boot/config-your-kernel-version (your distrib may or may not provide this).

As I can remember, it is an old (at least 5 years) feature, thus your kernel probably supports it.

Online ext4 resizement doesn't work with some highly finetuned mke4fs configurations (sorry I forgot exactly what - some of the ext4 fs flags makes it impossible).

I've been working on a bug related to this ext4 feature. So far as I can tell from the kernel source (linux 4.15.x) there is no feature called 'uninit_bg'.
It looks like it's just baked in to the ext4 filesystem, although the key feature in question is called 'lazy_itable_init'. There's be a few changes in this code and perhaps the comments + docs need to catch up with reality.

When using mkfs you can add the -E lazy_itable_init=0 option as other people has said - I don't think this attribute gets stored in the filesystem's metadata - the kernel thread for handling the lazy init is triggered or not dependent upon whether lazy_itable_init is set, but once all block groups on the FS have the ITABLE_ZEROED flag set then the filesystem is initialised and that's that - i.e. the method of initialisation stops being of any relevance.