[Novalug] best hard disk setup for home file server?
Bryan J. Smith
b.j.smith at ieee.org
Wed Oct 14 19:33:23 EDT 2009
Why not just keep them separate volume groups? I don't like
the idea of radically different disks in the same volume group,
regardless of how "well" it can optimize them.
Create two volume groups, one for each set of disks/arrays,
slice, format filesystems, mount and grow as needed. I do it
all-the-time with people who want single VGs and filesystems
for no reason.
Just the other day someone did something stupid and toasted
a filesystem. Guess what? It was only 300GB of their 6TB of
data and I got to have my silent "I told you so" because the other
5.7TB was unaffected by their screw up. Their argument was that
they may need to "grow" in the future. In reality, 50 million files
in a single filesystem is a bit of a headache anyway, and it's better
to keep a few million small files here, a few thousand big files that
are totally unrelated there, etc...
Filesystem mounts are extremely flexible. Bind mounts even
more so. I have a lot of different media under my base
/export/(servername)/static -- software, music, movies, etc...
Not all of it has to be the same filesystem, so it doesn't need
to be the same volume group either.
So I think you're a bit obsessed with making everything a single
volume group. I still strongly believe in the array:VG 1:1
relationship. Mixing disks that are "close enough" (same
capacity, similar spindle, different models) is one thing. But
trying to span over radically different arrays with very different
attributes to gain an unnecessary management benefit is not
something I push for.
That's really the only thing I'm a bit opinionated on. Choice of
disks and other things is one thing. But adding complexity into
a stack of layers that don't always work perfectly together when
one detail meshes poorly with another is not a fate I like to tempt.
----- Original Message ----
From: Richard Ertel <richard.ertel at gmail.com>
To: Bryan J. Smith <b.j.smith at ieee.org>
Cc: Brandon Saxe <brandon20va at yahoo.com>; novalug-bounces at calypso2.tux.org; Novalug <novalug at calypso2.tux.org>
Sent: Wed, October 14, 2009 7:25:46 PM
Subject: Re: [Novalug] best hard disk setup for home file server?
how tolerant of different sizes/speeds/models of drive is LVM2
mirroring/striping? if i had two 1TB drives and two 1.5TB drives,
mirrored and striped together, i'd have what, a single 2.5 TB array?
i DO like LVM quite a bit, so an opportunity to use it and have some
amount of fault tolerance is tempting.
On Wed, Oct 14, 2009 at 18:56, Bryan J. Smith <b.j.smith at ieee.org> wrote:
> Couple of notes ...
> - Only two (2) drives are required for RAID-0+1, mirrored, alternating stripes,
> although most implementations require four (4) drives. Although Linux mirroring
> typically requires a mirroring log, but it can reside on one of the two disks.
> - Software RAID-5 is fine for reads, and acts like RAID-0 minus one disk. RAID-6
> acts like RAID-0 minus two disks. But yes, for heavy writes, you've turned your
> interconnect into one of the most grossly inefficient "XOR engines." Sure, the CPU
> can churn out XORs fast, and even MMX makes it outstanding on blocks -- but the
> trip through the interconnect (gross if it's shared 133MBps 32-bit/33MHz PCI) and
> the LOAD-STO inefficiency (even with MMX) is nothing compared to XOR ASICs.
> Again, back to my analogy of GbE switch with an 8-bit 8051 microcontroller with
> an NPE ASIC doing MAC table lookups compared to a modern, 64-bit PC.
> - RAID-0, 1 and 0+1 can actually be done with DeviceMapper inside of LVM,
> without the need for MD.
> ----- Original Message ----
> From: Brandon Saxe <brandon20va at yahoo.com>
> (Linux software RAID supports this even though true RAID 10 needs 4 minimum)
> I recommend going RAID 10 if you're using software md. I'm using it with my 3 drives
> and it slaughters the performance of the RAID 5.
> If you really like LVM, then use it with RAID10 volumes where alignment is not as big\
> a deal as with RAID5/6.
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