[lug] LUG Digest, Vol 155, Issue 8

Will will.sterling at gmail.com
Wed Oct 12 22:04:31 MDT 2016

>From the lvmraid man page:


The 2.6.38-rc1 version of the Linux kernel introduced a device-mapper

target to interface with the software RAID (MD) personalities.  This
provided device-mapper with RAID 4/5/6 capabilities and a larger
development community.  Later, support for RAID1, RAID10, and RAID1E (RAID
10 variants) were added.  Support for these new kernel RAID targets was
added to LVM version 2.02.87.  The capabilities of the LVM \fBraid1\fP
type have surpassed the old \fBmirror\fP type.  raid1 is now recommended
instead of mirror.  raid1 became the default for mirroring in LVM version

On Wed, Oct 12, 2016 at 9:35 PM, Will <will.sterling at gmail.com> wrote:

> Do you have a definitive source on this?  The only sources I've seen
> making these claims didn't seem all to familiar with LVMs capabilities.
> On Thu, Sep 29, 2016 at 3:59 PM, Andrew Gilmore <agilmore2 at gmail.com>
> wrote:
>> From: Stephen Kraus <ub3ratl4sf00 at gmail.com>
>>> To: "Boulder (Colorado) Linux Users Group -- General Mailing List" <
>>> lug at lug.boulder.co.us>
>>> Cc:
>>> Date: Sat, 24 Sep 2016 15:21:25 -0400
>>> Subject: Re: [lug] RAID1 Versus Mirrored LVM (Fedora 23)
>>> I like RAID, but I also have a ZFS array. ZFS is generally faster, but
>>> its more dependant on you to ensure the viability of the array info and
>>> health.
>>> On Sep 24, 2016 11:09 AM, <stimits at comcast.net> wrote:
>>>> Hi,
>>>> It's becoming more obvious that I need to dig into details of LVM and
>>>> RAID. I had originally started out with the intent to produce a mirrored
>>>> RAID1 on two new disks, and then use that with LVM to divide up the content
>>>> between "/home" and "/var/www". None of those mount points require booting
>>>> to them, so this partially simplifies things.
>>>> Until recently I wasn't even aware that LVM itself can have physical
>>>> volumes combined into mirrored logical volumes in the same way as RAID1
>>>> does. So now I'm wondering if it would be wise to remove the RAID1+LVM
>>>> design and instead just use LVM with mirroring of two ordinary disk drives.
>>>> Is there anything special about reliability or performance...or anything
>>>> else...which would influence the choice of RAID1+LVM versus
>>>> LVM-with-mirroring? Why would I pick one scheme over the other?
>>>> Thanks!
>> After working through a few of these options, you should know that LVM
>> mirroring only uses the second mirror for reading if the first fails.
>> If you want RAID 1 read performance, don't use an LVM mirror.
>> Andrew
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