Re: LVM-Cache on fresh Ubuntu server install

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Author: Stephen Partington
Date:  
To: Main PLUG discussion list
Subject: Re: LVM-Cache on fresh Ubuntu server install
And i spoke too soon...

http://unix.stackexchange.com/questions/173704/booting-from-an-lvm-cached-volume

so now to get to a point where i can rebuild this or just reinstall from
scratch... i think the latter might be easier.

On Fri, Jul 8, 2016 at 11:41 AM, Stephen Partington <>
wrote:

> wow, that was much smoother than i thought it would be.
>
> I guess setting things up the way i have ahead of time was a good thing.
> now to move on to the rest of life. (also an interesting idea to set up a
> desktop/laptop this way to see how life works)
>
> lvm> vgs
>   VG     #PV #LV #SN Attr   VSize VFree
>   System   2   1   0 wz--n- 1.02t 1.38g
> lvm> pvs
>   PV         VG     Fmt  Attr PSize   PFree
>   /dev/sda3  System lvm2 a--  117.38g 1.38g
>   /dev/sdb2  System lvm2 a--  922.20g    0
> lvm> lvs
>   LV     VG     Attr       LSize   Pool    Origin         Data%  Meta%
>  Move Log Cpy%Sync Convert
>   System System Cwi-aoC--- 922.20g [cache] [System_corig] 0.00   0.70
>        0.00

>
>
> On Fri, Jul 8, 2016 at 11:24 AM, Stephen Partington <>
> wrote:
>
>> ​The biggest issue i have is that i am working with a mac mini. the 1T
>> drive is a 5400 rpm drive. this has been my home server for a while running
>> server 2016, but it is time to put something more useful on it.
>>
>> Part of this is specifically to learn how to use lvm and lvmcache.​ And
>> ram is on the list for this server just not in the budget yet.
>>
>> I am not worried about catastrophic failure or the like as nothing lives
>> on this server that does not already live anywhere else.
>>
>> I did the install with the Ubuntu server install so i could at least get
>> lvm set up partly ahead of time. so it looks like I am in a good place. I
>> was reading that article as i received your email.
>>
>> So now to extend the vg create the cache and meta lv's and turn things on.
>>
>> lvm> pvscan
>>   PV /dev/sdb2   VG System          lvm2 [922.20 GiB / 0    free]
>>   PV /dev/sda3                      lvm2 [117.38 GiB]
>>   Total: 2 [1.02 TiB] / in use: 1 [922.20 GiB] / in no VG: 1 [117.38 GiB]
>> lvm> pvs
>>   PV         VG     Fmt  Attr PSize   PFree
>>   /dev/sda3         lvm2 ---  117.38g 117.38g
>>   /dev/sdb2  System lvm2 a--  922.20g      0
>> lvm> vgs
>>   VG     #PV #LV #SN Attr   VSize   VFree
>>   System   1   1   0 wz--n- 922.20g    0
>> lvm> vgdisplay
>>   --- Volume group ---
>>   VG Name               System
>>   System ID
>>   Format                lvm2
>>   Metadata Areas        1
>>   Metadata Sequence No  2
>>   VG Access             read/write
>>   VG Status             resizable
>>   MAX LV                0
>>   Cur LV                1
>>   Open LV               1
>>   Max PV                0
>>   Cur PV                1
>>   Act PV                1
>>   VG Size               922.20 GiB
>>   PE Size               4.00 MiB
>>   Total PE              236082
>>   Alloc PE / Size       236082 / 922.20 GiB
>>   Free  PE / Size       0 / 0

>>
>>
>> On Fri, Jul 8, 2016 at 11:02 AM, Matt Graham <>
>> wrote:
>>
>>> On 2016-07-08 10:00, Stephen Partington wrote:
>>>
>>>> 1T spinning disk and 128G SSD installed. [...] going with LVM-Cache
>>>> Sadly the Ubuntu server installation does not have the option of
>>>> setting up LVM for anything other than its most basic configuration
>>>>
>>>
>>> LVM is complicated, and using LVM-cache is a bit more complicated than
>>> just making some PVs and putting them into a VG and then making LVs.
>>>
>>> What I understand about LVM is that you can build your LVM group and
>>>> then migrate/expand it without a full install/wipe or 3rd disk device
>>>> to host your core os installation. Can this be done for LVM cache as
>>>> well?
>>>>
>>>
>>> Yes. Your setup would be something like this: 2 PVs, one on the fast
>>> disk, one on the slow disk[0]. One VG with both PVs in it. Multiple LVs.
>>> One named root on the fast disk (mounted at / obviously), one small one
>>> named cache-meta on the fast disk, one larger one named cache on the fast
>>> disk, and finally one larger one named origin on the slow disk. You'd
>>> probably mount the last one on /data or /home or wherever makes sense to
>>> put the large amount of stuff you want to serve up. I suppose you could
>>> put / on the spinny-disk and use almost all of the SSD for cache too. Your
>>> call.
>>>
>>> If you already have some PVs and LVs set up, you might need to use
>>> pvmove and lvresize and resize2fs to resize filesystems and LVs and move
>>> them to the appropriate PV. These things are of course doable from a
>>> running system and should not cause any problems.
>>>
>>> https://rwmj.wordpress.com/2014/05/22/using-lvms-new-cache-feature/
>>> describes all the commands you'd need to run to make this stuff happen.
>>> And getting an additional 4G or 8G of RAM might help more than using an SSD
>>> as a cache, depending on what exactly is going on.
>>>
>>> (I haven't actually tried this, but I've got a 32G unused partition on
>>> my SSD right now, and this could be a fun weekend project. I will let you
>>> know if I run into any problems.)
>>>
>>> [0] With 1T disks as cheap as they are, consider a softRAID-1 instead of
>>> a single spinny disk. Disk failures are No Fun At All.
>>>
>>> --
>>> Crow202 Blog: http://crow202.org/wordpress
>>> There is no Darkness in Eternity
>>> But only Light too dim for us to see.
>>> ---------------------------------------------------
>>> PLUG-discuss mailing list -
>>> To subscribe, unsubscribe, or to change your mail settings:
>>> http://lists.phxlinux.org/mailman/listinfo/plug-discuss
>>>
>>
>>
>>
>> --
>> A mouse trap, placed on top of your alarm clock, will prevent you from
>> rolling over and going back to sleep after you hit the snooze button.
>>
>> Stephen
>>
>>
>
>
> --
> A mouse trap, placed on top of your alarm clock, will prevent you from
> rolling over and going back to sleep after you hit the snooze button.
>
> Stephen
>
>



--
A mouse trap, placed on top of your alarm clock, will prevent you from
rolling over and going back to sleep after you hit the snooze button.

Stephen
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