Hi,
On my x86_64 system I have a SiL311x controller that can do RAID. If I configure my 2 identical disks in a RAID1 setup, I would expect to see only 1 block device on Linux. Still I see 2 block devices.
Is this intentional, and if so, isn't that dangerous ? (i.e. writing to both disks at the same time)
Anyone with an insight, please explain :)
-- dag wieers, dag@wieers.com, http://dag.wieers.com/ -- [all I want is a warm bed and a kind word and unlimited power]
On Sunday 19 June 2005 00:58, Dag Wieers wrote:
Hi,
On my x86_64 system I have a SiL311x controller that can do RAID. If I configure my 2 identical disks in a RAID1 setup, I would expect to see only 1 block device on Linux. Still I see 2 block devices.
Is this intentional, and if so, isn't that dangerous ? (i.e. writing to both disks at the same time)
Anyone with an insight, please explain :)
-- dag wieers, dag@wieers.com, http://dag.wieers.com/ -- [all I want is a warm bed and a kind word and unlimited power] _______________________________________________
Not REAL RAID - requires a Windoze driver to make it work. Software RAID is your friend unless you want to spring for a 3ware card (not cheap).
HTH Brian
On Sun, 19 Jun 2005, Brian Parish wrote:
On Sunday 19 June 2005 00:58, Dag Wieers wrote:
On my x86_64 system I have a SiL311x controller that can do RAID. If I configure my 2 identical disks in a RAID1 setup, I would expect to see only 1 block device on Linux. Still I see 2 block devices.
Is this intentional, and if so, isn't that dangerous ? (i.e. writing to both disks at the same time)
Anyone with an insight, please explain :)
Not REAL RAID - requires a Windoze driver to make it work. Software RAID is your friend unless you want to spring for a 3ware card (not cheap).
Ok, that's what I was suspecting, as I noticed now that the VIA SataRaid has the same problem :) Now I understand why people said that some of these devices are not real hardware RAID, this works because it needs a special driver. (I never understood how a hardware component could do that, but never thought about specialized drivers)
I'm used to ServeRAID.
So whatever I configure in the BIOS, it has no effect on Linux, right ?
Thanks, -- dag wieers, dag@wieers.com, http://dag.wieers.com/ -- [all I want is a warm bed and a kind word and unlimited power]
On Sunday 19 June 2005 01:47, Dag Wieers wrote:
On Sun, 19 Jun 2005, Brian Parish wrote:
On Sunday 19 June 2005 00:58, Dag Wieers wrote:
On my x86_64 system I have a SiL311x controller that can do RAID. If I configure my 2 identical disks in a RAID1 setup, I would expect to see only 1 block device on Linux. Still I see 2 block devices.
Is this intentional, and if so, isn't that dangerous ? (i.e. writing to both disks at the same time)
Anyone with an insight, please explain :)
Not REAL RAID - requires a Windoze driver to make it work. Software RAID is your friend unless you want to spring for a 3ware card (not cheap).
Ok, that's what I was suspecting, as I noticed now that the VIA SataRaid has the same problem :) Now I understand why people said that some of these devices are not real hardware RAID, this works because it needs a special driver. (I never understood how a hardware component could do that, but never thought about specialized drivers)
I'm used to ServeRAID.
So whatever I configure in the BIOS, it has no effect on Linux, right ?
Thanks, -- dag wieers, dag@wieers.com, http://dag.wieers.com/ -- [all I want is a warm bed and a kind word and unlimited power] _______________________________________________
No, you can change BIOS settings until your fingers bleed without making any difference. In fact Linux pretty much ignores most of what's in the BIOS in any case. Very handy when wanting to put large drives in old systems!
not necessarily. I had a friend put linux on his computer but his bios doe snot support 48 bit LBA so he only saw 30 gigs both in the bios and in linux itself.
Brian Parish wrote:
On Sunday 19 June 2005 01:47, Dag Wieers wrote:
On Sun, 19 Jun 2005, Brian Parish wrote:
On Sunday 19 June 2005 00:58, Dag Wieers wrote:
On my x86_64 system I have a SiL311x controller that can do RAID. If I configure my 2 identical disks in a RAID1 setup, I would expect to see only 1 block device on Linux. Still I see 2 block devices.
Is this intentional, and if so, isn't that dangerous ? (i.e. writing to both disks at the same time)
Anyone with an insight, please explain :)
Not REAL RAID - requires a Windoze driver to make it work. Software RAID is your friend unless you want to spring for a 3ware card (not cheap).
Ok, that's what I was suspecting, as I noticed now that the VIA SataRaid has the same problem :) Now I understand why people said that some of these devices are not real hardware RAID, this works because it needs a special driver. (I never understood how a hardware component could do that, but never thought about specialized drivers)
I'm used to ServeRAID.
So whatever I configure in the BIOS, it has no effect on Linux, right ?
Thanks, -- dag wieers, dag@wieers.com, http://dag.wieers.com/ -- [all I want is a warm bed and a kind word and unlimited power] _______________________________________________
No, you can change BIOS settings until your fingers bleed without making any difference. In fact Linux pretty much ignores most of what's in the BIOS in any case. Very handy when wanting to put large drives in old systems! _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
On Sat, 2005-06-18 at 11:56 -0400, William Warren wrote:
not necessarily. I had a friend put linux on his computer but his bios doe snot support 48 bit LBA so he only saw 30 gigs both in the bios and in linux itself.
Check the jumpers on the disk. Some have an option to limit the number of heads reported to 16 (not 255) and/or cylinders to 1024. That would cause an issue.
BTW, the ATA28 (28-bit) limitation is _not_ 33.8GB (32GiB), it's:
16,384 cylinders (14-bit) 63 sectors/cylinder (6-bit) 255 heads (8-bit) 512 bytes/sector ======== 137GB (128GiB) (14-bit + 6-bit + 8-bit = 28-bit)
Now if you're limiting heads to 16 (instead of 255), that can cause the limitation by which the maximum number of cylinders is 65,536 (16-bit) because some OSes have a limitation on the number of cylinders in their geometry.
65,536 cylinders (16-bit) 63 sectors/cylinder (6-bit) 16 heads (5-bit, 10000, instead of all 1s) 512 bytes/sector ======== 33.8GB (32GiB)
That's a common issue cause by the disk being jumpered to report only 16 heads.
On Sun, 2005-06-19 at 01:52 +1000, Brian Parish wrote:
No, you can change BIOS settings until your fingers bleed without making any difference. In fact Linux pretty much ignores most of what's in the BIOS in any case. Very handy when wanting to put large drives in old systems!
Actually, NT ignores it too _until_ you load the vendor's "FRAID" driver. If you boot on any NT kernel (NT4SP4+), it will see the "raw" disks as well.
Only DOS kernels (Win9x/Me) will see the RAID configuration as a disk in "MS-DOS compatibility mode."
On Sat, 2005-06-18 at 16:58 +0200, Dag Wieers wrote:
Hi, On my x86_64 system I have a SiL311x controller that can do RAID. If I configure my 2 identical disks in a RAID1 setup, I would expect to see only 1 block device on Linux. Still I see 2 block devices. Is this intentional, and if so, isn't that dangerous ? (i.e. writing to both disks at the same time) Anyone with an insight, please explain :)
They are _not_ RAID, they are what I call "Fake/Free RAID" (FRAID).
The BIOS just allows you to designate the disks as RAID-1 (simple mirroring) or organize the blocks into RAID-0 (stripped). Once the OS loads, it not only needs to know that so it doesn't see the disks as "just a bunch of disks," but so it knows how to write the data as such. That is done 100% in the OS driver.
Since that logic is typically licensed from the same 2-3 3rd parties, and those 3rd parties make royalties on those sales, it is _never_ going to be GPL.
Now there is a "clean-room" GPL RAID logic in "ataraid.c" in the kernel. And then there are "card interface" sister drivers in "hptraid.c" (HPT), "pdcraid.c" (Promise) and "silraid.c" (Silicon Image), but they _rarely_ work well. Little changes and differences in the cards, drivers, etc... always seem to cause all sorts of issues when I've tried them.
_Real_ hardware RAID cards _never_ talk directly to the ATA channels. They _always_ have _all_ communication between the system and the ATA channels go through an "on-board intelligence" like an i960 microcontroller in the Promise SuperTrak, Adaptec 2400/2800A, LSI Logic MegaRAID 320-4 and 320-6, an XScale superscalar microcontroller in the LSI Logic MegaRAID 320-8X, or an ASIC in the 3Ware Escalade and NetCell SR-series.
For more on ATA RAID, see the article "Dissecting ATA RAID Options" in 2004 April "Sys Admin" magazine. The article is not available on-line, but if you subscribe to Sys Admin, you get a CD with _all_ back issues of Sys Admin and Perl Journal: http://www.samag.com/articles/2004/0404/
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Brian Parish -
Bryan J. Smith -
Dag Wieers -
William Warren