[Novalug] best hard disk setup for home file server?

Richard Ertel richard.ertel@gmail.com
Wed Oct 14 19:45:56 EDT 2009


you keep coming up with obvious solutions that my brain somehow skips
over. it seems to be in my nature to over-complicate things in an
effort to reach some kind of nirvana.

these 1.5 TB drives that i claimed are flaky could be ok, as one has
passed the "Long DST" test in Seatools. once i get all the data onto
the backup, i'll try the other tests that are not read-only. if these
drives are ok, i think my plan is to get a PCI SATA controller, and
just make 3 mirrored LVM2 arrays, one with two 1TB drives, one with
these two 1.5TB drives, and one with two yet-to-be-purchased
not-seagate 1.5TB drives.

On Wed, Oct 14, 2009 at 19:33, Bryan J. Smith <b.j.smith@ieee.org> wrote:
> 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@gmail.com>
> To: Bryan J. Smith <b.j.smith@ieee.org>
> Cc: Brandon Saxe <brandon20va@yahoo.com>; novalug-bounces@calypso2.tux.org; Novalug <novalug@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@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@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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