Re: Advice on hardware server to use for small a dedicated data center

[Miles Fidelman <mfidelman@meetinghouse.net>]

On 6/29/20 9:10 AM, Dan Ritter wrote:

> Miles Fidelman wrote:
> > Just to be clear... mdadm is NOT raid - it's an admin program for managing
> > linux raid (md) devices.?? And then you need to worry about LVM (logical
> > volume manager), and a network file system on top of them.
> Just to be clear, you are being pedantic bordering on wrong here. This
> is like saying "a hamburger is not ground beef patties, and then you
> need to worry about vegetables and condiments".
>
> mdadm is the administrative interface program for the kernel's md
> subsystem. It is used generically as a synonym for "the kernel's
> md subsystem" because for most people encountering them, they
> are inextricably intertwined.
>
> The kernel's md subsystem manages RAID 0, 1, 4, 5, 6 and 10. It
> also has a non-RAID linear mode, a container abstraction, and a
> fault-simulation mode.

Now who's being pedantic?

And isn't this exactly what I said?  mdadm is an admin program, it 
doesn't perform the raid function.

> LVM is completely independent of the md subsystem, and can be
> used with or without it. Some people love it. Some avoid it like
> the plague -- oops. Some avoid it like rational people avoid the
> plague.
>
> Various network file systems are also completely independent of
> the md subsystem.
> ZFS is an integrated data storage system that presents N
> filesystem and partition-equivalent views to the kernel. It is
> independent of and an alternative to md and lvm. It offers a
> semi-integrated NFS and CIFS export facility. Underneath, it
> offers storage options including error-detection, compression, mirroring,
> striping, RAID-5 and -6 style parity, read caching and write
> caching. Only the error detection is mandatory.
I'm pretty sure we all know this.  The point is that comparing mdadm to 
ZFS is an apples to oranges comparison.  You don't chose between mdadm 
and ZFS, you chose between ZFS and a stack of software that performs the 
same set of functions.

Miles Fidelman


--
In theory, there is no difference between theory and practice.
In practice, there is.  .... Yogi Berra

Theory is when you know everything but nothing works.
Practice is when everything works but no one knows why.
In our lab, theory and practice are combined:
nothing works and no one knows why.  ... unknown