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 at 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 at 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
Bryan J. Smith
2005-Jun-18 16:05 UTC
[CentOS] SiL311x SataRaid (sata_sil) -- sata_sil != RAID
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/ -- Bryan J. Smith b.j.smith at ieee.org --------------------------------------------------------------------- It is mathematically impossible for someone who makes more than you to be anything but richer than you. Any tax rate that penalizes them will also penalize you similarly (to those below you, and then below them). Linear algebra, let alone differential calculus or even ele- mentary concepts of limits, is mutually exclusive with US journalism. So forget even attempting to explain how tax cuts work. ;->