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#1 2009-11-21 15:39:16

ctarwater
Member
Registered: 2009-02-05
Posts: 300

FakeRaid (raid0) Basic questions

I have absolutely no experience with Raid.  None. 

A friend was interested in trying out Arch and he came over last night so we could have a few beers and I could help him through his first Arch install - usually a fairly painless process.  Once he got here he told me he likes using a raid0 setup for the performance/speed benefits (I won't argue the validity of this statement)

Anyhow, after multiple hours of trying we couldn't figure the damned thing out.  We'd get everything seemingly setup but could never get grub installed.

We're trying to install arch on a setup of two 350bg hard drives.
The raid0 setup is done through his Asus Bios.

1) Is this step from the wiki necessarry?  # modprobe sata_sil (or whatever chipset driver you need)  If so, how do we find what chipset driver to use?  As far as we can tell it's "isw" but no combo of isw/sata_isw modules could be found.

2) Partitioning scheme?  He doesn't plan to use swap and plans on putting everything in one partition.  Do we need a seperate partition for /boot?

3) Anyone have any advice for just using a livedisc with gparted to setup the drives ahead of time?

Thanks all!

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#2 2009-11-21 16:14:21

llcawthorne
Member
From: Columbia, SC
Registered: 2009-10-16
Posts: 142

Re: FakeRaid (raid0) Basic questions

Last I heard, grub doesn't support booting from RAID for /boot (except for md1 mdadm style mirrors).

isw?  Is that Intel matrix raid?  Not sure, sounds familiar.  I've got an Asus board with that stuff, but use mdadm instead since I don't need windows to access my RAID array, and I couldn't get grub to boot off my fakeraid setup.  If you use fakeraid, you have to put your boot somewhere else (last I checked).  I remember playing around with ways to make it work at some point, and not finding anything that I could easily implement.  YMMV.

Here's a good walkthrough on the wiki with mdadm raid though.  The too are roughly equivalent ways of doing the same thing in my opinion.  I have loaded both and done speed tests with bonnie, and both are noticeably faster than no software RAID but not very different from one another to my eye.

I am pretty sure I referred to it for my setup:
http://wiki.archlinux.org/index.php/Ins … AID_or_LVM

In my current setup, I have three separate partitions on each of three separate disks.  One set of 256M partitions that is part of an md1 array that makes up boot, one set of 8G partitions that make up a raid0 array that is swap (they really could have been in the LVM), and three 950Gish partitions that make up a md0 array that I have setup as the pv of an lvm set so I can flexibly reparition it as the need arises. 

You don't have to go LVM on the main partition though, I just did since I mess around a bit and like the flexibility with having so much room.


To understand recursion, you must understand recursion.

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#3 2009-11-21 16:28:16

ctarwater
Member
Registered: 2009-02-05
Posts: 300

Re: FakeRaid (raid0) Basic questions

you know, based on the error grub was giving us, it would make sense that we couldn't boot from raid.

isw is indeed an intel based thing from his asus board. 

When you say i have to "have to put your boot somewhere else" do you mean a different partition or a different hard drive?  (sorry, like I said, I don't understand Raid at all)  Or can Raid still work as long as both hard drives are partitioned exactly the same?  i.e. both have a /boot partition and both have /

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#4 2009-11-21 17:10:50

llcawthorne
Member
From: Columbia, SC
Registered: 2009-10-16
Posts: 142

Re: FakeRaid (raid0) Basic questions

If you want to use the fakeraid, as far as I know, the boot partition has to exist somewhere off the array (wherever that might be..  another drive, a usb thumbdrive, a floppy if anyone still has them).  The drive can still be hooked up to the same controller even, BIOS just cannot consider it part of the array.  It can't just be a different partition, because once you give the drive to BIOS as a fakeraid drive, it takes the whole thing (or at least does with my setup).

Ex:  When I played with fakeraid a bit, I had my boot parition on my 120 GB SATA drive and my array was made up of my 3 1TB WD hard drives.

But then I switched to mdadm, and now my boot is a mirrored partition that exists on each of my 3 1 TB hard drives.  Two separate RAID0 striped paritions hold swap and the lvm that contains my OS's & data.

Both ways to work, but I get a bit more control with mdadm, and it tends to be more widely used so is easier to find info on in my experience.  I think mdadm was slightly faster also (but not by very much).  I might still have the document around here somewhere that I kept my notes in if you are interested...


To understand recursion, you must understand recursion.

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#5 2009-11-21 17:55:44

ctarwater
Member
Registered: 2009-02-05
Posts: 300

Re: FakeRaid (raid0) Basic questions

Thanks for the info.  I'd love a copy of your notes if you can find it.

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#6 2009-11-21 18:36:19

llcawthorne
Member
From: Columbia, SC
Registered: 2009-10-16
Posts: 142

Re: FakeRaid (raid0) Basic questions

I know I said I would only post this if you were interested, but now that I've gone and dug it up...   (Oh, good.  It looks like you confirmed you were interested while I was typing this.  Thanks!)

Yeah, I actually had more data that I thought.  This was on my old PC, so I believe the array was just two drives.  Here's some a link that should work to pull up some of the results.  My main purpose was to compare encrypted speed with unencrypted speed for simple tests (bonnie & cp), and I did some dmraid/mdadm comparisons while I was messing around.  After looking at everything, I think I forgot about the results and just did what I planned to in the first place (run mdadm, since I liked the amount of info available, and use lvm so I could split things up, and then go about my day). 

I'm not claiming this is any grand revelation about anything.  Just some things I did and results I wrote down.  Take them as you will.

http://llcawthorne.is-a-geek.org/raid-p … scheme.txt

For comparison sake, here's a bonnie of my current three drive array with WD Black's (mdadm - xfs) [on a different computer]:

Version 1.03e       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
darktower    24016M 128900  99 195100  13 80437   7 68759  74 213183   7 276.2   0
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16  6968  27 +++++ +++  6744  18  7382  26 +++++ +++  5150  14
darktower,24016M,128900,99,195100,13,80437,7,68759,74,213183,7,276.2,0,16,6968,27,+++++,+++,6744,18,7382,26,+++++,+++,5150,14

And a timed copy of a bit over 7G of data from my XFS data lv to my EXT4 home lv

time cp -r Led\ Zeppelin/ Nine\ Inch\ Nails/ Pink\ Floyd/ Disturbed/ Tool/ A\ Perfect\ Circle/ Ozzy\ Osbourne/ /home/cawthorn/test/

real    1m22.716s
user    0m0.043s
sys    0m7.200s

The same copy from my XFS data lv to my NTFS ide hard drive

real    1m40.420s
user    0m0.087s
sys    0m7.866s

To my NTFS sata non-RAID member hard drive

real    1m58.808s
user    0m0.097s
sys    0m8.006s

Copy the same data from my non-RAID sata drive to my non-RAID IDE drive

real    2m40.553s
user    0m0.140s
sys    0m7.473s

Oh well, some data, some differences.  Some may be unique to my config, and some may be filesystem/drive layout differences.  Big difference in copy speeds on my new rig it would seem.  The old system had an array of what I am now using as my single non-RAID SATA drive, as I recall (I dropped one member of the array while I was doing something else <butterfingers>, so had to go raidless until I built a new computer).

Either way, if I am copying large amounts of data, I go browse the web or get a drink or use the bathroom in real life, so cp results aren't that important.  Response time is more interesting, but how it translates to any real improvement when I know my computer is spending the large majority of its time waiting on me rather than vice-versa is quite debateable.

Note to Self: I should get rid of spaces from directories in my music folder.


To understand recursion, you must understand recursion.

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#7 2009-11-27 06:19:58

BeRReGoN
Member
Registered: 2008-03-28
Posts: 35

Re: FakeRaid (raid0) Basic questions

ctarwater wrote:

1) Is this step from the wiki necessarry?  # modprobe sata_sil (or whatever chipset driver you need)  If so, how do we find what chipset driver to use?  As far as we can tell it's "isw" but no combo of isw/sata_isw modules could be found. Add dmraid to hook in mkinitcpio.conf before filesystem. No need to add dm_mod in modules since dmraid load it.

2) Partitioning scheme?  He doesn't plan to use swap and plans on putting everything in one partition.  Do we need a seperate partition for /boot?

3) Anyone have any advice for just using a livedisc with gparted to setup the drives ahead of time?

With the intel chipset, you don't need the sata_sil, just modprobe dm_mod and do dmraid -ay and you should see your array. dmraid is already installed in the last installation image.   

The boot partition isn't necessary but when you follow the wiki, it might be less confusing using it.

You can use cdfisk /dev/mapper/<your_raid> to partition your raid.


The install after is pretty simple, follow the wiki but i don't know why the chroot, just enter the grub install mode and if like me it fails when you do setup (hd0) try setup --stage2=/dev/mapper/<nom de partition> (hd0)

You might have to do a setup (hd0) and reboot if you boot in grub install mode the first time.

If you understand french, their wiki is less confusing:
http://wiki.archlinux.fr/install/fakeraid

Last edited by BeRReGoN (2009-11-27 06:21:50)

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#8 2009-12-04 12:41:44

loosec
Member
Registered: 2007-03-08
Posts: 134

Re: FakeRaid (raid0) Basic questions

Yes you can have everything on one partition using dmraid.

Also Fake Raid wikipage now updated and cleaned.

Only messy part now is the GRUB installation but it still works even if it's hacky. Berregons alternative to grub install is most likely very much more correct. Feel free to improve the wiki with it. smile

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