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x0054
*nix forums beginner
Joined: 21 Feb 2006
Posts: 20
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 Posted: Mon Jul 10, 2006 11:57 pm Post subject:
Software vs. Hardware RAID 1
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I am building a SFF server for my apartment. The case I picked has 2 HD
bays which I intend to fill with 2 ATA100 250GB drives. The motherboard has
2 ATA133/100 IDE buses.
If I go with Software RAID1 I would have HD1 as master on the primary IDE
bus and HD2 as master on secondary IDE bus with the CD drive as slave on
the same bus.
What I am wondering is how would Software RAID1 compare with HW RAID1 and
if there are any significant advantages or drawbacks to either? Also, is it
a problem that HD2 will share IDE bus with my CD drive? (I only really
going to use the CD drive to install linux)
Thank you,
- Bogdan |
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Dances With Crows
*nix forums Guru
Joined: 01 Mar 2005
Posts: 328
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| Posted: Tue Jul 11, 2006 1:21 am Post subject:
Re: Software vs. Hardware RAID 1
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["Followup-To:" header set to comp.os.linux.hardware.]
On 10 Jul 2006 23:57:22 GMT, x0054 staggered into the Black Sun and
said:
| Quote: | 2 HD bays which I intend to fill with 2 ATA100 250GB drives. The
motherboard has 2 ATA133/100 IDE [channels]. If I go with Software
RAID1 I would have HD1 as master on the primary IDE bus and HD2 as
master on [the] secondary IDE bus, with the CD drive as slave on the
same bus.
What I am wondering is how software RAID1 [compares] with HW RAID1
and if there are any significant advantages or drawbacks to either.
|
SoftRAID-1 will probably be *faster* than doing RAID in hardware.
Hardware RAID generally uses a fairly slow dedicated bit of silicon.
SoftRAID uses the main CPU, which is A) damn fast and B) usually idle in
a modern machine. The main problem is that softRAID is a bit less
transparent than hardware RAID. Just read the RAID HOWTO and you'll be
fine. Also remember that you'll probably need to copy the first 63
sectors of /dev/hda to /dev/hdc manually with dd, since softRAID doesn't
mirror the bootloader, just the partitions.
| Quote: | Also, is it a problem that HD2 will share [an] IDE [channel] with my
CD drive? I [am] only really going to use the CD drive to install
linux.
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This shouldn't matter on a modern board, so long as you're not using the
CD-R* much. Only one device per IDE channel can be active at once,
thanks to IDE's designed-in brain damage, so your softRAID won't be
fully R while your CD-R* is running. HTH,
--
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see
Brainbench MVP for Linux Admin / mail: TRAP + SPAN don't belong
http://www.brainbench.com / "He is a rhythmic movement of the
-----------------------------/ penguins, is Tux." --MegaHAL |
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x0054
*nix forums beginner
Joined: 21 Feb 2006
Posts: 20
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| Posted: Tue Jul 11, 2006 2:26 am Post subject:
Re: Software vs. Hardware RAID 1
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Dances With Crows <danSPANceswitTRAPhcrows@gmail.com> wrote in
news:slrneb5vkk.fcs.danSPANceswitTRAPhcrows@samantha.crow202.dyndns.org:
| Quote: | ["Followup-To:" header set to comp.os.linux.hardware.]
On 10 Jul 2006 23:57:22 GMT, x0054 staggered into the Black Sun and
said:
2 HD bays which I intend to fill with 2 ATA100 250GB drives. The
motherboard has 2 ATA133/100 IDE [channels]. If I go with Software
RAID1 I would have HD1 as master on the primary IDE bus and HD2 as
master on [the] secondary IDE bus, with the CD drive as slave on the
same bus.
What I am wondering is how software RAID1 [compares] with HW RAID1
and if there are any significant advantages or drawbacks to either.
SoftRAID-1 will probably be *faster* than doing RAID in hardware.
Hardware RAID generally uses a fairly slow dedicated bit of silicon.
SoftRAID uses the main CPU, which is A) damn fast and B) usually idle
in a modern machine. The main problem is that softRAID is a bit less
transparent than hardware RAID. Just read the RAID HOWTO and you'll
be fine. Also remember that you'll probably need to copy the first 63
sectors of /dev/hda to /dev/hdc manually with dd, since softRAID
doesn't mirror the bootloader, just the partitions.
Also, is it a problem that HD2 will share [an] IDE [channel] with my
CD drive? I [am] only really going to use the CD drive to install
linux.
This shouldn't matter on a modern board, so long as you're not using
the CD-R* much. Only one device per IDE channel can be active at
once, thanks to IDE's designed-in brain damage, so your softRAID won't
be fully R while your CD-R* is running. HTH,
|
Thanks, that sounds great. Yeah, actually I probably would disconnect
the CD-ROM after install all together. Really the only reason for it is
to load Debian.
I looked though SW RAID setup, and it looks very straight foreword. The
one other question I had had to do with booting. You mentioned that I
would need to copy over, or maybe install, bootloader on both drives.
When setting up bootloader would I tell it to boot from hda or hdc, or
can I specify md0 (the SW raid disk)?
If I specify the actual disk I would have to change it respective to the
disk. Right? So on hda the bootloader would be set to boot from hda and
on hdc it would be set to hdc?
Thanks again for the help,
- Bogdan |
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Walter Mautner
*nix forums Guru Wannabe
Joined: 25 Feb 2005
Posts: 210
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| Posted: Tue Jul 11, 2006 6:27 am Post subject:
Re: Software vs. Hardware RAID 1
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x0054 wrote:
| Quote: | I am building a SFF server for my apartment. The case I picked has 2 HD
bays which I intend to fill with 2 ATA100 250GB drives. The motherboard
has 2 ATA133/100 IDE buses.
If I go with Software RAID1 I would have HD1 as master on the primary IDE
bus and HD2 as master on secondary IDE bus with the CD drive as slave on
the same bus.
No problem then. |
| Quote: | What I am wondering is how would Software RAID1 compare with HW RAID1 and
if there are any significant advantages or drawbacks to either? Also, is
it a problem that HD2 will share IDE bus with my CD drive? (I only really
going to use the CD drive to install linux)
Most of the times you are better off with sw raid1: linux can boot from it, |
even when one drive goes tits up, but you need to initiate a resync
manually after changing the faulty drive.
A software raid *can* lock up when a hd dies on the job or locks the ide
controller. You may have to physically unplug the ide cable of the
defective drive to be able to reboot.
The advantage of sw raid (mdadm setup with persistent superblocks) is, you
can have multiple partitions with differen raid strategy (raid1
for /, /usr, /home, raid0 for /var and /tmp as an example), and you can
move the disks to another mainboard with a different ide/sata controller if
yours breaks. Which may become difficult with onboard hw raid.
Beware: most onboard "hw raid" is actually "hostraid": the bios can create
and format a raid set, and work with dos - but for windows you need
F6/install driver, similar for linux if available. *And* you are lost when
your old mobo breaks 2 years later without identical replacement available.
Same goes for pci hw raid controllers, though they are moveable to a new
board. These are not dirt cheap though ...
--
vista policy violation: Microsoft optical mouse detected penguin patterns
on mousepad. Partition scan in progress to remove offending
incompatible products. Reactivate MS software.
Linux 2.6.16-mm1,Xorg7.0 [LinuxCounter#295241,ICQ#4918962] |
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Dances With Crows
*nix forums Guru
Joined: 01 Mar 2005
Posts: 328
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| Posted: Tue Jul 11, 2006 5:47 pm Post subject:
Re: Software vs. Hardware RAID 1
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On 11 Jul 2006 02:26:01 GMT, x0054 staggered into the Black Sun and said:
| Quote: | Dances With Crows <danSPANceswitTRAPhcrows@gmail.com> wrote:
x0054 wrote:
What I am wondering is how software RAID1 [compares] with HW RAID1
and if there are any significant advantages or drawbacks to either.
SoftRAID-1 will probably be *faster* than doing RAID in hardware.
The main problem is that softRAID is a bit less transparent than
hardware RAID. Just read the RAID HOWTO and you'll be fine.
Thanks, that sounds great. Yeah, actually I probably would disconnect
the CD-ROM after install all together. Really the only reason for it
is to load Debian.
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It'd probably be a good idea to keep the CD-R* connected, because it's a
pain to reconnect it if you need it later. And you probably will at
some point.
| Quote: | I looked though SW RAID setup, and it looks very straightforward.
When setting up [the] bootloader, would I tell it to boot from hda or
hdc, or can I specify md0 (the SW raid disk)?
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GRUB and LILO don't grok RAID. You'd install the bootloader to /dev/hda
(or (hd0) ) and pass the "root=/dev/md0" option to the kernel. Like so:
machine:~# grub
grub> root(hdX,Y) # replace with numbers of /boot partition
grub> setup(hd0) # install bootloader to MBR of first disk
grub> quit # done; write or modify grub.conf to taste
Of course, you'll have to have softRAID-1 built in to the kernel or
available in the initrd for that to work. The default Debian kernel has
those things available, just remember to build that stuff in when you
compile a custom kernel.
| Quote: | If I specify the actual disk I would have to change it respective to
the disk. Right? So on hda the bootloader would be set to boot from
hda and on hdc it would be set to hdc?
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What? Install the bootloader on /dev/hda, use dd to copy the first 63
sectors to /dev/hdc . If /dev/hda dies and you have to reboot, you're
going to have to switch some cables around, but you'd have to do that
*anyway* because you'd be replacing the dead disk. HTH,
--
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see
Brainbench MVP for Linux Admin / mail: TRAP + SPAN don't belong
http://www.brainbench.com / "He is a rhythmic movement of the
-----------------------------/ penguins, is Tux." --MegaHAL |
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Andrew Gideon
*nix forums Guru Wannabe
Joined: 30 Mar 2005
Posts: 116
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| Posted: Sat Jul 15, 2006 10:02 pm Post subject:
Re: Software vs. Hardware RAID 1
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On Tue, 11 Jul 2006 08:27:52 +0200, Walter Mautner wrote:
| Quote: | raid0 for /var and /tmp as an example),
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Just a nit: I'd not RAID0 those as they're needed to boot. But I agree
with the basic principle of having a choice with mdadm. We often do that
with workstations, where the "main" volumes are mirrored but all the
work/test areas are just striped.
| Quote: | and you can
move the disks to another mainboard with a different ide/sata controller
if yours breaks. Which may become difficult with onboard hw raid.
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That is an excellent point. It's the "opposite" of the logic I use for
preferring external RAID on servers over internal: if the machine fails, I
can just shift the RAID volumes to a different server.
- Andrew |
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John-Paul Stewart
*nix forums Guru
Joined: 20 Feb 2005
Posts: 497
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| Posted: Sun Jul 16, 2006 7:49 pm Post subject:
Re: Software vs. Hardware RAID 1
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Andrew Gideon wrote:
| Quote: | On Tue, 11 Jul 2006 08:27:52 +0200, Walter Mautner wrote:
raid0 for /var and /tmp as an example),
Just a nit: I'd not RAID0 those as they're needed to boot.
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Neither /var nor /tmp is needed to boot. Some stuff (daemons in
particular) like to write to /var/run or somesuch on startup, but those
things should fail gracefully without /var. Moreover, booting to single
user mode (e.g., for maintenance/recovery) shouldn't require /var or
/tmp at all. Those two are often on their own filesystems (which means
they're not guaranteed to be mounted) so I see no harm in putting them
on a RAID-0 array. |
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