ext4 filesystem

[caj]

Hi,

1) I would like to know if any one is using ext4 with RHEL5u6?

2) Are we going to get the real performance improvement when compared with the ext3.


3) I red in some places due to the delayed allocation there could be some dta loss (files becomes 0) upon system crash? Is that still there with ext4 ?

4) How about the ext4 file system with LVM striping?

What are the other things we need to take care if we are using ext4?

Your replay will be much appreciated

Thanks

[caj]

Hi ,

Could you please someone respond to my query .

Are we started using ext4 in producton ?

[dirk dierickx]

don't worry about it, ext4 is just fine.

performance gains will be noted when performing actions on large files, that use was greatly optimized by ext4.

[caj]

But on RHEL 5u6 we cannot create ext4 on vg00 ,as Anacoda install won't support this type of install .

So Can I create other filesystem with ext4 while I am keeping all vg00 filesystem on ext3 ?

Thanks

[Matti_Kurkela]

Yes, you can.

In RHEL 6, you can use ext4 on installation too. Apparently RedHat didn't want to change the OS installer too much in the middle of the lifetime of RHEL 5.

The ext4 filesystem was introduced to RHEL 5 as a Technology Preview in RHEL 5u3; it was refreshed in 5u4, and became a fully supported filesystem in 5u6.

MK

[caj]

Thanks MK for your response .

How do I use ext4 for vg00?

Do you think it is good idea to specify the kickstart file with ext4 file system for vg00 ?

And how about the data loss due to delayed allocation? Is it still there? or any patch/workaround has been implemented by redhat ?

I see sometime back people were facing the truncated file after the system crash .Is still be a problem?

is People started using ext4 for the production environment ?

[Matti_Kurkela]

The "data loss due to delayed allocation" problem was fixed in mainline kernel version 2.6.30, although some distributions have backported the fix to earlier kernel versions like 2.6.28 or 2.6.29.

(see: http://en.wikipedia.org/wiki/Ext4 )

Because of this, I would strongly prefer RHEL 6 over RHEL 5 when using ext4: RHEL 6 has kernel version 2.6.32.

On RHEL 5, I would not recommend using ext4 on the system VG, since if you have to boot the system from the installation DVD to rescue mode, the rescue mode might not recognize ext4. Also, the GRUB boot loader in RHEL 5 may not recognize ext4, so at least the /boot filesystem must remain ext3.

But if you really want, you could convert the ext3 filesystems on vg00 to ext4 after installation. See this HOWTO:

https://ext4.wiki.kernel.org/index.php/Ext4_Howto#Converting_an_ext3_filesystem_to_ext4

RHEL 5u6 Technical Notes says:
"As of Red Hat Enterprise Linux 5.6 the ext4 file system is fully supported. However, provisioning ext4 file systems with the anaconda installer is not supported, and ext4 file systems need to be provisioned manually after the installation. "

This means:
- make sure you have the e4fsprogs package installed (yum install e4fsprogs)

- create a separate LV (and an entire VG, if you want) for your application and/or data, using system-config-lvm or the commands pvcreate/vgcreate/lvcreate, as you prefer.

- create an ext4 filesystem on the data LV:
mkfs.ext4 /dev/vgdata/lvol1

- add it to /etc/fstab, specifying filesystem type as "ext4".

We're currently testing ext4 on RHEL6 using a 10 TB filesystem, because that's what the customer requested. Apparently the customer's application cannot handle having data on multiple filesystems (wtf??? I think this is an attempt to use a filesystem where a database would be more suitable, but whatever...).

So far it seems to work just fine, although creating the filesystem took quite a while. Once the customer has accumulated enough test data to fill it to at least about 2/3 full, we're going to run a full filesystem check and see how much time it requires.

MK