A few remaining questions about installing to RAID-10

I'm setting up new linux boxes, hoping to install whatever OS I choose
to a software RAID array.

I've got 4 identical SATA drives, and would ideally like to use RAID-10=


I've read a bunch of slightly stale How-To docs, and have a few questio=
ns.

(1) Can Linux boot from /boot on RAID-10? =A0Oldest info I found said n=
o
boot from RAID at all, then more recent docs said boot from RAID-1
works. =A0I found nothing on RAID-10. =A0What's the latest sccop on thi=
s?

(2) As far as I can tell, none of the installers in Centos, Ubuntu or
Opensuse are RAID-10 aware. =A0Seems like the sanest way to get setup
would be to boot from SystemRescueCD, do the partitioning and RAID
creation, then re-boot from an installer disk using the pre-setup
disks.

Am I missing some other, simpler approach?

(3) Assuming that I'll have to boot from RAID-1 (Just suspect that
RAID-10 is not yet an option for /boot, but willing to be shown
wrong!), I'm considering 3 partitioning/raid_config options,

=A0(a)
=A0 =A0DISK1 =A0 =A0 =A0DISK2 =A0 =A0 =A0DISK3 =A0 =A0 =A0DISK4
=A0 [ RAID-1 =A0/boot =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0]
=A0 [ RAID-1 =A0swap =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ]
=A0 [ RAID-10 LVM, /root & 'other' parts =A0 ]

=A0(b)
=A0 =A0DISK1 =A0 =A0 =A0DISK2 =A0 =A0 =A0DISK3 =A0 =A0 =A0DISK4
=A0 [ RAID-1 =A0/boot =A0] =A0 =A0[ RAID-1 =A0swap =A0 ]
=A0 [ RAID-10 LVM, /root & 'other' parts =A0 ]

=A0(c)
=A0 =A0DISK1 =A0 =A0 =A0DISK2 =A0 =A0 =A0DISK3 =A0 =A0 =A0DISK4
=A0 [ RAID-1 =A0/boot =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0]
=A0 [ RAID-10 LVM, /root, swap & 'other' =A0 ]

Are there any clear benefits/concerns of one config over the other?

(4) In setting up the RAID arrays, I've got a choice of metadata
versions. =A0It seems that the distros' installers default to "1.0", bu=
t
that "1.1" & "1.2" are both available, too.

Should I just use the newest, 1.2? =A0Any problems if I do?

(5) In whatever config is "best" in (3), above, is it still good
advice to install the bootlader into multiple MBRs? For example, if I
extend the RAID-1 over all 4-disks, then, I install the loader into
all four MBRs?

I think these are the last details I need to iron out before getting st=
arted.

Thanks for any help!

Ben
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RE: A few remaining questions about installing to RAID-10

WAT?! How can I mount an unpartitioned/unformatted array? This is more direct than using a filesystem, although there would be no journalling, right? If I were to mount my small disk for / and the unpartitioned array as /home for example.

Seems like journalling/crash recovery is pretty vital. Could not partitioning be recommendable?


--- On Mon, 10/5/09, Leslie Rhorer wrote:
> Partitions are not needed at all unless your underlying
> topology requires
> it:
>
> `mdadm --create --raid-devices=2 --metadata=1.0 --chunk=128
> --level=1
> /dev/md0 /dev/sda /dev/sdb`
>
> Will work just fine. You can also
> use LVM with raw disks. Both
> systems simply stitch together storage units provided by
> the drive
> subsystem, so any block device found in /dev can be
> used. Once the array is
> assembled, it is not necessary to partition it, either,
> again unless your
> overlaying topology requires it. On my systems, the
> boot drives are
> partitioned to allow booting into Windows if necessary, and
> usually the swap
> is also in a partition on the boot drive, but my arrays are
> completely
> un-partitioned.
>
>



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Re: A few remaining questions about installing to RAID-10

> WAT?!  How can I mount an unpartitioned/unformatted array?  =
This is more direct than using a filesystem, although there would be no=
journalling, right?  If I were to mount my small disk for / and t=
he unpartitioned array as /home for example.

What's he's saying is that RAID and LVM do not need partitions to work
properly. You can create a raid array on the raw(unpartitioned)
/dev/sdX devices and then create a LVM volume group using a physical
volume(PV) on a raw(unpartitioned) /dev/mdX (RAID) device.

The filesystem still needs a partition/volume but that can created
either by partitioning /dev/mdX *or* creating a logical volume in LVM.

=46or example, on my system at home I use RAID-6 created using
/dev/sd[b-f]. The resulting /dev/md0 acts as a physical volume for LVM
and I've created several Logical Volumes aka "partitions" for the
filesystems to reside in.

> Seems like journalling/crash recovery is pretty vital.  Could no=
t partitioning be recommendable?

See above. You still have a partition/volume of some sort where the
filesystem is created.


--=20
Drew

"Nothing in life is to be feared. It is only to be understood."
--Marie Curie
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Re: A few remaining questions about installing to RAID-10

--- On Mon, 10/5/09, Drew wrote:
> > Seems like journalling/crash recovery is pretty vital.
> Could not partitioning be recommendable?
>
> See above. You still have a partition/volume of some sort
> where the
> filesystem is created.

.... But no journalling for crash recovery?

Can this be recommendable? If no answer I presume not.



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Re: A few remaining questions about installing to RAID-10

> ... But no journalling for crash recovery?

Journalling is a function of the filesystem, not the block devices.
RAID is there to make sure you won't lose data if a physical disk
dies.



--
Drew

"Nothing in life is to be feared. It is only to be understood."
--Marie Curie
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RE: A few remaining questions about installing to RAID-10

> -----Original Message-----
> From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
> owner@vger.kernel.org] On Behalf Of adfas asd
> Sent: Monday, October 05, 2009 10:31 AM
> To: linux-raid@vger.kernel.org
> Subject: RE: A few remaining questions about installing to RAID-10
>
> WAT?! How can I mount an unpartitioned/unformatted array? This is more

I didn't say "unformatted". Mkfs does not require a partition, but
you're going to need a file system if you are going to have files.

> direct than using a filesystem, although there would be no journalling,
> right?

Journaling is a facility of the file system, not the partition. If
you install a journalled file system, then you will have a journal. If you
install something like ext2, then you won't. I happen to be using XFS,
which is a journalling file system, on my video server and the backup server
arrays.

> If I were to mount my small disk for / and the unpartitioned array
> as /home for example.

In your case it may not make too much difference, as I take it the
system is not logged into by anyone but you (or am I mistaken?), but I would
generally speaking shy away from putting /home in anything which might not
be available at login time, or which is likely to be taken offline when the
system is up and running. It can be done, of course, but logins can be a
bit problematical for ordinary users when /home is not present. That said,
yes, the small disk can be / and the array can be /home. I don't recommend
running without swap, so if the small disk is the only other physical drive,
then it does need to be partitioned at a minimum into your main space and
some swap. A separate /boot partition is not a terrible idea, either,
especially on a multi-boot system. I have some systems with a separate
/boot partition and some without. Sometimes there is a really good reason
to make /var a separate partition, but in your case I think not.

> Seems like journalling/crash recovery is pretty vital. Could not
> partitioning be recommendable?

Not for that purpose, no. They have nothing to do with one another.
Partitioning allows a single disk to have multiple mount points, or to boot
more than one OS, or to allow multiple file systems serving different
purposes to all reside on a single physical disk. Journalling creates a
cache for writes which allows a file system to better survive a dirty
shutdown without corrupting the file system. The journal can be on the same
physical disk as the file system or a completely separate disk system. It
can be on a separate partition, but it is not required.


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RE: A few remaining questions about installing to RAID-10

> > WAT?! =A0How can I mount an unpartitioned/unformatted array? =A0Thi=
s is more
> direct than using a filesystem, although there would be no journallin=
g,
> right? =A0If I were to mount my small disk for / and the unpartitione=
d array
> as /home for example.
>=20
> What's he's saying is that RAID and LVM do not need partitions to wor=
k
> properly. You can create a raid array on the raw(unpartitioned)
> /dev/sdX devices and then create a LVM volume group using a physical
> volume(PV) on a raw(unpartitioned) /dev/mdX (RAID) device.

True, but it is simpler than that. Partitions are not needed in
general unless one needs to create a separate task space on a single dr=
ive
volume. If one has no swap space, then it is entirely possible to run =
a
Linux system with no partitions at all. The file system can be created=
on a
raw disk, and as long as the MBR is good and the boot loader can read t=
he
file system, you're good. Note I don't genrally recommend running with=
out a
swap space, and going to extra trouble just to prevent partitioning is =
not
very productive, but there is no reason to partition a drive if it is n=
ot
necessary, whether the "drive" is a single physical disk or an array.

> The filesystem still needs a partition/volume but that can created
> either by partitioning /dev/mdX *or* creating a logical volume in LVM=


It doesn't need a partition, just a block device. That device can
be a partition on a disk, a whole disk, or an array.

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Re: A few remaining questions about installing to RAID-10

       True, but it is simpler than that.  Pa=
rtitions are not needed in
> general unless one needs to create a separate task space on a single =
drive
> volume.  If one has no swap space, then it is entirely possible =
to run a
> Linux system with no partitions at all.  The file system can be =
created on a
> raw disk, and as long as the MBR is good and the boot loader can read=
the
> file system, you're good.  Note I don't genrally recommend runni=
ng without a
> swap space, and going to extra trouble just to prevent partitioning i=
s not
> very productive, but there is no reason to partition a drive if it is=
not
> necessary, whether the "drive" is a single physical disk or an array.

I did not know that. I always assumed that for physical disks you
needed a partition of some sort so the filesystem doesn't stomp all
over the boot sector (where used).That said I think I'll stick to
partitioning my boot drive. Feels safer somehow.

>> The filesystem still needs a partition/volume but that can created
>> either by partitioning /dev/mdX *or* creating a logical volume in LV=
M.
>
>        It doesn't need a partition, just a block =
device.  That device can
> be a partition on a disk, a whole disk, or an array.

I forgot you can do that with mdX. It's been a while since I've made
filesystems (other then boot drives) without LVM.


--=20
Drew

"Nothing in life is to be feared. It is only to be understood."
--Marie Curie
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RE: A few remaining questions about installing to RAID-10

> > necessary, whether the "drive" is a single physical disk or an arra=
y.
>=20
> I did not know that. I always assumed that for physical disks you
> needed a partition of some sort so the filesystem doesn't stomp all
> over the boot sector (where used).

If the boot sector is not used, though, and there is no swap on the
drive, then partitioning is not absolutely required. If the MBR is use=
d,
then indeed one must make sure the file system doesn't stomp on it.

> That said I think I'll stick to
> partitioning my boot drive. Feels safer somehow.

Oh, I agree, without question. I'm a big fan of a small boot drive
with 3 or 4 partitions and one or more arrays with no partitions at all=


> >> The filesystem still needs a partition/volume but that can created
> >> either by partitioning /dev/mdX *or* creating a logical volume in =
LVM.
> >
> > =A0 =A0 =A0 =A0It doesn't need a partition, just a block device. =A0=
That device
> can
> > be a partition on a disk, a whole disk, or an array.
>=20
> I forgot you can do that with mdX. It's been a while since I've made
> filesystems (other then boot drives) without LVM.

Yep. Sure can. I've used LVM, and for some applications it's
great. Indeed, as I mentioned, adfas might be well served with LVM vol=
umes
on each machine. It certainly would provide great performance, althoug=
h as
I also mentioned, I don't think drive performance is really his problem=
, per
se.

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Re: A few remaining questions about installing to RAID-10

>        Yep.  Sure can.  I've used LVM, =
and for some applications it's
> great.  Indeed, as I mentioned, adfas might be well served with =
LVM volumes
> on each machine.  It certainly would provide great performance, =
although as
> I also mentioned, I don't think drive performance is really his probl=
em, per
> se.

I follow the threads on the MythTV list so I'd agree there are better
ways to partition/RAID the system. The MythTV guys are, in many cases,
pushing Terabytes of data through consumer grade SATA drives, RAID,
LVM and high performance filesystems like JFS/XFS. It's amazing
sometimes the extent they go to tuning their rigs to handle the
various on-disk buffers and what not MythTV seems to use.

Adfas: You may want to consider talking with the boys over at MythTV.
If you want to tune your rig for MythTV those guys are the best ones
to talk with as they know their app very well.


--=20
Drew

"Nothing in life is to be feared. It is only to be understood."
--Marie Curie
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Re: A few remaining questions about installing to RAID-10

On Mon, Oct 05, 2009 at 08:42:22PM -0700, Drew wrote:
> > =A0 =A0 =A0 =A0Yep. =A0Sure can. =A0I've used LVM, and for some app=
lications it's
> > great. =A0Indeed, as I mentioned, adfas might be well served with L=
VM volumes
> > on each machine. =A0It certainly would provide great performance, a=
lthough as
> > I also mentioned, I don't think drive performance is really his pro=
blem, per
> > se.
>=20
> I follow the threads on the MythTV list so I'd agree there are better
> ways to partition/RAID the system. The MythTV guys are, in many cases=
,
> pushing Terabytes of data through consumer grade SATA drives, RAID,
> LVM and high performance filesystems like JFS/XFS. It's amazing
> sometimes the extent they go to tuning their rigs to handle the
> various on-disk buffers and what not MythTV seems to use.
>=20
> Adfas: You may want to consider talking with the boys over at MythTV.
> If you want to tune your rig for MythTV those guys are the best ones
> to talk with as they know their app very well.

Are there any conclusions from the mythtv group?

Best regards
keld
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Re: A few remaining questions about installing to RAID-10

Thanks for the input guys. Wish I could get similar info for my NAS thread.


--- On Mon, 10/5/09, Drew wrote:

> From: Drew
> Subject: Re: A few remaining questions about installing to RAID-10
> To: linux-raid@vger.kernel.org
> Date: Monday, October 5, 2009, 8:42 PM
> > Yep. Sure can.
> I've used LVM, and for some applications it's
> > great. Indeed, as I mentioned, adfas might be well
> served with LVM volumes
> > on each machine. It certainly would provide great
> performance, although as
> > I also mentioned, I don't think drive performance is
> really his problem, per
> > se.
>
> I follow the threads on the MythTV list so I'd agree there
> are better
> ways to partition/RAID the system. The MythTV guys are, in
> many cases,
> pushing Terabytes of data through consumer grade SATA
> drives, RAID,
> LVM and high performance filesystems like JFS/XFS. It's
> amazing
> sometimes the extent they go to tuning their rigs to handle
> the
> various on-disk buffers and what not MythTV seems to use.
>
> Adfas: You may want to consider talking with the boys over
> at MythTV.
> If you want to tune your rig for MythTV those guys are the
> best ones
> to talk with as they know their app very well.
>
>
> --
> Drew
>
> "Nothing in life is to be feared. It is only to be
> understood."
> --Marie Curie
> --
> To unsubscribe from this list: send the line "unsubscribe
> linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>



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Re: A few remaining questions about installing to RAID-10

MythTV? Go away, come back & it appears my thread's been hijacked
without a 2nd thought :-(
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RE: A few remaining questions about installing to RAID-10

--- On Mon, 10/5/09, Leslie Rhorer wrote:
> Indeed, as I mentioned, adfas might be well
> served with LVM volumes
> on each machine. It certainly would provide great
> performance, although as
> I also mentioned, I don't think drive performance is really
> his problem, per
> se.

Hang on a sec. LVM would make it easy to add drives. And as I understood it, you recommend a RAID in the garage and another in the HTPC, LVMed together? Well with this I could add another array, but that's not what's needed. I'd need to add a drive to the garage and another to the HTPC, which means each of those arrays would need to be completely reconstructed.

OTOH if I set up the garage as an LVM and the HTPC as another, then RAID those LVMs together, maybe I could add a drive to each LVM... AS LONG AS I add the same size drive to BOTH the garage and HTPC for expansion? And no need to completely reconstruct the RAID array?



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RE: A few remaining questions about installing to RAID-10

I apologize for the late reply. In all the myriad e-mail I get, I
missed this one.

> --- On Mon, 10/5/09, Leslie Rhorer wrote:
> > Indeed, as I mentioned, adfas might be well
> > served with LVM volumes
> > on each machine. It certainly would provide great
> > performance, although as
> > I also mentioned, I don't think drive performance is really
> > his problem, per
> > se.
>
> Hang on a sec. LVM would make it easy to add drives. And as I understood
> it, you recommend a RAID in the garage and another in the HTPC, LVMed
> together?

No. I am suggesting an LVM volume in the HTPC and an LVM volume in
the garage. 'No RAID at all.

> Well with this I could add another array, but that's not what's
> needed. I'd need to add a drive to the garage and another to the HTPC,
> which means each of those arrays would need to be completely
> reconstructed.
>
> OTOH if I set up the garage as an LVM and the HTPC as another, then RAID
> those LVMs together, maybe I could add a drive to each LVM... AS LONG AS I
> add the same size drive to BOTH the garage and HTPC for expansion? And no
> need to completely reconstruct the RAID array?

That might be possible. I don't really recommend it, but it might
be made to work.

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