Deciphering the Proper LVM

MikeyD

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Hey guys,

My experience with logical volume managers (lvms) is limited. I've often added drives and extended them at work using cloud VMs, but beyond that I've never had to resize, remove or really "manage" them (just delete VM when I'm done with it :p)

I have a home server running CentOS 6. I set up an LVM when I first built it but as a less-informed Linuxer at the time and just want to see what you guys think of the setup and if it should be changed. I'm looking into it more now as I just bought a 4 TB HDD I want to add.


Current Disks:
/dev/sda - 64 GB SSD - assigned to lv_root (supposedly for /, but also has boot sector)
/dev/sdb - 2 TB HDD - assigned to lv_home (supposedly for /home)

Adding a 4 TB HDD to extend /home dirs.


My VG/PV/LV and df -h output is below:
vgdisplay:
Code:
--- Volume group ---
  VG Name               vg_charlie
  System ID
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  7
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               3
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               1.88 TiB
  PE Size               4.00 MiB
  Total PE              492070
  Alloc PE / Size       491923 / 1.88 TiB
  Free  PE / Size       147 / 588.00 MiB
  VG UUID               89FdWQ-xFkj-oTLQ-r93N-SR5N-oCk1-a04klF

pvdisplay:
Code:
[[email protected]: /dev/vg_charlie]# pvdisplay
  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               vg_charlie
  PV Size               59.14 GiB / not usable 4.00 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              15138
  Free PE               0
  Allocated PE          15138
  PV UUID               XvQPeA-IZCU-Bz4o-Ok1d-JtZn-vjYr-mIDGy6

  --- Physical volume ---
  PV Name               /dev/sdb
  VG Name               vg_charlie
  PV Size               1.82 TiB / not usable 1.09 MiB
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              476932
  Free PE               147
  Allocated PE          476785
  PV UUID               bxJTA5-h0Me-ahUK-EP7H-Hxvk-U0YG-Yc8lDI

lvdisplay:
Code:
[[email protected]: /dev/vg_charlie]# lvdisplay
  --- Logical volume ---
  LV Path                /dev/vg_charlie/lv_root
  LV Name                lv_root
  VG Name                vg_charlie
  LV UUID                GizFrC-I1Lw-3hjF-iUMd-bvWc-Ez09-0DYyn6
  LV Write Access        read/write
  LV Creation host, time charlie, 2014-07-29 17:56:22 -0400
  LV Status              available
  # open                 1
  LV Size                48.45 GiB
  Current LE             12402
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

  --- Logical volume ---
  LV Path                /dev/vg_charlie/lv_home
  LV Name                lv_home
  VG Name                vg_charlie
  LV UUID                4dJHsn-dDLn-ya4q-0IFC-1nRK-s2yi-ulUUpc
  LV Write Access        read/write
  LV Creation host, time charlie, 2014-07-29 17:56:43 -0400
  LV Status              available
  # open                 1
  LV Size                1.82 TiB
  Current LE             477995
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:2

  --- Logical volume ---
  LV Path                /dev/vg_charlie/lv_swap
  LV Name                lv_swap
  VG Name                vg_charlie
  LV UUID                njaAy6-ef9w-t9pi-dFxF-tNH8-Ja4b-Qyhi2e
  LV Write Access        read/write
  LV Creation host, time charlie, 2014-07-29 17:56:46 -0400
  LV Status              available
  # open                 1
  LV Size                5.96 GiB
  Current LE             1526
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

df -h:
Code:
[[email protected]: /dev/vg_charlie]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_charlie-lv_root
                       48G  5.1G   41G  12% /
tmpfs                 3.8G  164K  3.8G   1% /dev/shm
/dev/sda1             477M  169M  283M  38% /boot
/dev/mapper/vg_charlie-lv_home
                      1.8T  1.5T  262G  86% /home


I wanted to check a few things:

1. I've heard its not a good idea to set up an LVM for disks at different r/w speeds. Is it a better idea not to have SSD and HDDs on the same LVM?

2. Ideally I want root (/) on the SSD and /home on the HDDs. According to df -h that looks like it is correct, but can I trust df -h with an LVM? Since I wouldn't think they are directly 'mounted'.

3. I also noticed there is a swap logical volume but can't really tell what disk it was created with. Is there a command to check?

4. I'm thinking of upgrading the OS to Centos 7 since 6 is quickly reaching EOL, maybe even doing a fresh install so I can use disk encryption. Is there a good way or resource anyone has on the best way to "break up" an LVM? I'd be worried of file corruption on files that extend to multiple physical disks but maybe this isn't a problem since each disk is part of its own logical volume?


Sorry in advance for the barrage of info and questions :). Really also just looking for general advice on if and how others have set up LVMs, particularly with different disk types.

Thanks!

Mike
 
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MikeyD

MikeyD

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Looking at this today pretty sure I was overthinking this lol.
 

Rob

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Hey there!

Yeah, if you're thinking of upgrading to CentOS 7 anyway, i'd save your files somewhere, then start from scratch and set up LVM the way you see yourself using it in the future since you can't do a direct 6 --> 7 upgrade anyway.

I wouldn't mix speeds or hardware types of drives in LVM, though it may just default to the lowest in the end anyway.

On the other hand, since a full wipe / re-install is in your future at some point, why not experiment w/ the dif speeds and arch of the drives within lvm.. it might end up being interesting. :)

Let us know what you end up doing!
 
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