Let say that my installation of 1708 went well and then the update to 1810 went well also.
I'm stuck on several issues:

When I 'cat /etc/fstab" I see "UUID=099d7278-4cb9-434a-b933-c684434d6365 /boot ext defaults 1 2"
But when I enter 'df -h' I see " /dev/md126 2.0G 270M 1.6G 15% /boot"
When I comment out the UUID line and add the /dev/md126 I get an error - sometimes (requires a boot to rescue go back to the UUID, so there it sits).

When I installed CentOS 6 it allowed me to control the name of the MD devices for both /boot and the LVM raid devices. Why not with CentOS 7?

Why is it when I install CentOS 7 over an existing CentOS 6 file systems (I want to keep the allocations the same) CentOS 7 really doesn't like it??? I found myself deleting and reallocating the same partitions. Especially the /boot raid-1 allocations - it always comes up as 'unknown' .

I guess I'm old school because I like the flow of CentOS 6 as-far-as disks are concerned (i..e. allocate raid device from first disk; allocate raid device from second disk; create raid partition by adding the 2 raid devices; label it as /dev/md0 with a mount point of /boot; etc). CentOS 7 just seems odd they way it's done. What I did learn is that on the allocation screen under 'name' is where I put the lv_name. Why doesn't it just say so? Is there a place where I can place the MD name (i.e. /dev/md1 etc.)?

Can someone help me understand why it's like this?

TIA
Gene

You need this command:

Did you take a look at the guide for the RAID? I am unable to help much because I've never used RAID this way. I have always had RAID managed by a storage appliance and then plugged virtual disks into the system via iscsi.

RAID guide here: https://docs.centos.org/en-US/centos...ide/Steps-x86/

On that same link it reads this about upgrading from Centos 6 to 7:

So the guide actually advises against upgrading from Centos6, which is a bit annoying but I suppose better in the long run. There's a few changes in Centos7 which make living with 7 a bit better / easier and if your server applications depend on functions available in 6 which arent there in 7 then that would be tricky to manage.

This is so because df doesn't report the UUID of the filesystem. It identifies filesystems by their device file only.
This could be related to the fact that /dev/md126 is a non-persistent device file name, meaning that there is no guarantee it will be called /dev/md126 next time you boot.
Admittedly, I have never tried installation on RAIDs, so I can't comment on this.
What makes you think CentOS 7 doesn't like existing CentOS 6 file systems?

are you asking Ned for help in understanding something, or is that a typo?
who is Ned?

I think I can help with some of these issues.
First - In the title should have been 'Need' not 'Ned'.
Second - The problem with the /boot is because the system is using those generated MD names (i.e. MD124, MD125, etc) and they are not guaranteed to be the same between boots. This all goes back to the disk naming - under CentOS 6 the disks named /dev/sda, /dev/sdb, /dev/sdc, etc may not be the same physical disks as with CentOS 7. I learned this when I had issues with a machine that has 4 physical 1 TB drives all WD black. Under CentOS 6 the disk named /dev/sda did not have the same serial number as CentOS 7 /dev/sda - had to start tracking what disk was where by serial number. If you use the UUID definition you will always get the correct /boot.
Third - I think (no proof) that there are backward compatibility issues for the raid-1 definitions between CentOS 6 and CentOS 7 that only show up on the /boot definition.

On my test machine I tried to enter /dev/md0 in the 'label' field and boot in the 'name' field and it didn't like it there. I was OK with putting 'lv_usr' in the 'name' field for the vg_opsys volume group, but not '/dev/md1' in the 'label' field.

I don't have any other ideas to give.

TIA
Sandy

Let me say this first - Gene is my cousin (hence the same last name).

Gene manages just 8 CentOS machines and one of those is a spare that he is using to migrate/move to CentOS 7. His issues stem from the fact that he doesn't have a SAN; NAS; or any device where the storage is outside of the physical machines. He has some scripts he has built over time that are dependent on things being the same across all 8 machines (why is the device that was /dev/sda under CentOS 5 now /dev/sdb under CentOS 7? Why is /dev/md0 under CentOS 6 now /dev/md124 under CentOS 7 - for this boot but may be /dev/md127 the next boot?). Also why hasn't CentOS progressed to the point where a disk drive larger than 2 TB be used during install? I know why - it's because CentOS uses fdisk. shouldn't fdisk be upgraded or change and use gdisk (gdisk work from the smallest to at least 10 TB drives).

He started with RHEL 2.1 when you could get it and not pay for support (the same for RHEL 4). But moved to CentOS 5 when paying for support became mandatory. But at least most everything was consistent.

He asked why doesn't CentOS 7 support BluRay devices (he thought great idea for backups - 25 GB or 50 GB- great). But the best answer was to update to a version 4 custom kernel - bad idea when you have 50 machines to maintain - what if you have 500 machines???

He is becoming frustrated and I can't seem to help him.

Sandy

sjpoole12 - no worries. I came here because I don't mind to offer help where I can. But I am no linux expert. Actually, I have spoken with berndbausch many times on Openstack (thanks again berndbausch ) and he is more of an expert. And I've reported the unhelpful person above (as I have done others here), like why even comment? Seems the many thousands of posts is irrelevant, so don't take offence.

May be it would help if some more context was given about what was trying to be done here?

Regarding the fdisk / 2TB limitation, I'm not sure but in my dealings with Red Hat it seems that they can make changes if the majority require it. May be it's just that no one has requested something like this yet or only a few have... But any change will probably take a while anyway.

Unfortunately I think that with Centos7, you might ned to change some things on your side.

Regarding SAN / NAS, Red Hat actually have guides on how to create yourself a SAN. I was looking to do this myself, but then came across cheap open-source SANs that utilise technology that is found in the high-end storage appliances. Such as NVRAM and flash paired up with SSD storage or spinning drives. The idea here with this is that the disk writes are responded to immediately even though they're not written to disk. This gives the OS the appearance of super fast storage writes. The storage manages the actual writes to disk in a batch, so it queues them up and writes all at once.

If you dont want to use that, then oVirt free virtualisation can use internal storage and then you can utilise storage snapshots of the virtual disk. There are also P2V tools available that will allow you to boot the physical system from CDROM, and send all of the data on the physical disks over to ovirt as a virtual disk. You can have mutliple hosts (physical machines) with their own separate internal storages also (ovirt 4.3).

Lastly, could you use a USB backup drive instead of blueray?

Again it's difficult to propose anything specific as I'm not sure exactly what your goals are. I hope that this post has been helpful to you guys.

OK, So far I think I've solved all of my hard drive issues!
What I did was to reinstall CentOS 6 because I can define everything just like I want it to be.
The hard drive environment is:
2 - 120 GB WD SATA Drives
4 - 4 TB WD SATA Drives
On the 120 GB drives I've defined the following RAID-1 devices:
/dev/md0 - /dev/sda1 | /dev/sdb1 - /boot - 2 GB
/dev/md1 - /dev/sda2 | /dev/sdb2 - /dev/vg_osswap/ 32 GB - lv_sysswap 16 GB - swap
/dev/md2 - /dev/sda3 | /dev/sdb3 - /dev/vg_opsys/ 78 GB - lv_root 8 GB - /name I entered lv_sysswap
- lv_archive 2 GB - /archive
- lv_home 4 GB - /home
- lv_opt 2 GB - /opt
- lv_tmp 5 GB - /tmp
- lv_usr - 12 GB - /usr
- lv_usr_local 2 GB - /usr/local
- lv_var 8 GB - /var

On the 4 - 4 TB dribes I've defined the following RAID-10 device:
/dev/md3 - /dev/sd(c-f)1 - /dev/vg_sysdata 7.28 TB - Many lv_ devices.

The definitions for /dev/md0; /dev/md1; /dev/md2 are built from a custom kickstart DVD that was built from RHEL 4 and constantly modified since then so it works with CentOS 6. However, I do not have custion install DVD for CentOS 7 so I have to do the install manually.

When I did the CentOS 7 1708 install and I got to the 'Custom Partition' page I did the following:
The allocation for /boot shows up as 'unknown' so I entered the mount point as /boot; I selected reformat as ext4; it did show up as raid 1; in the label I entered /dev/md0; in the name I entered boot.
The allocation for swap shows up as CentOS 6.10 so there was no mount point; reformated as swap; in the label I entered /dev/md1; in the name I entered lv_sysswap.
For all of the other defined OS file systems I added the mount points; reformatted as ext4; they showed up as raid-1 but in the label I entered /dev/md2 for all of them; in the name I entered the lv name as shown above.
What was strange was that when I did the raid-10 file systems there was information in the label and name fields already.

So going forward I will continue to use the 1708 DVD after I verify that all of the allocations are basically the same across board.

I think I understand as much as I need to at this point. I would like to see a document explaining all of this I've encountered.

Gene