raw devices and Linux

I know this must be asked over and over, but I'm setting up Foundation 2000 on Caldera Linux eServer 2.3 and I had some questions about raw devices: 1. The machine notes say that Linux doesn't support raw devices. A tech support person said that this was because Linux handles raw devices in a non-standard way, but that a new version of Linux to come out "soon" would fix this problem. Has anyone heard anything more specific about this? 2. Parts of the Admin Guide to IDS 9.2 say that performance with cooked files rather than raw devices can be worse by orders of magnitude. Has anyone found this to be true? 3. Assuming that Linux does gain the ability to use raw devices with Informix, the Admin Guide says that chunks are max 2 Gb big and that offsets are max 2 Gb. My disks are 18 Gb. Am I correct in thinking that there would be no way to use them as Informix raw devices (except for the first 2 Gb) without using my SCSI card to RAID them and present them as a large number of 2 Gb logical drives?

Hi! Re: 3) The same problem exists with SCO where combination of partition size and division only can give you 7 pieces of max 2 GB = 14 GB. The solution is to create multiple partition on the drive ( each < 14 GB) and divide them into up to seven pieces. Each partition ends up as a unix device and has a unique name. Other questions left to Linux gurus. HTH Michael Richard Puchalsky wrote: > I know this must be asked over and over, but I'm setting up Foundation 2000 > on Caldera Linux eServer 2.3 and I had some questions about raw devices: > > 1. The machine notes say that Linux doesn't support raw devices. A tech > support person said that this was because Linux handles raw devices in a > non-standard way, but that a new version of Linux to come out "soon" would > fix this problem. Has anyone heard anything more specific about this? > > 2. Parts of the Admin Guide to IDS 9.2 say that performance with cooked > files rather than raw devices can be worse by orders of magnitude. Has > anyone found this to be true? > > 3. Assuming that Linux does gain the ability to use raw devices with > Informix, the Admin Guide says that chunks are max 2 Gb big and that offsets > are max 2 Gb. My disks are 18 Gb. Am I correct in thinking that there > would be no way to use them as Informix raw devices (except for the first 2 > Gb) without using my SCSI card to RAID them and present them as a large > number of 2 Gb logical drives?

In article <38FA17A7.8C2129D8@sqlcanada.com>, Michael Krzepkowski <michaelk@sqlcanada.com> writes >Hi! > >Re: 3) The same problem exists with SCO where combination of partition size >and division only can give you 7 pieces of max 2 GB = 14 GB. The solution >is to create multiple partition on the drive ( each < 14 GB) and divide them >into >up to seven pieces. Each partition ends up as a unix device and has a unique >name. > >Other questions left to Linux gurus. > >HTH > >Michael > > >Richard Puchalsky wrote: > >> I know this must be asked over and over, but I'm setting up Foundation 2000 >> on Caldera Linux eServer 2.3 and I had some questions about raw devices: >> >> 1. The machine notes say that Linux doesn't support raw devices. A tech >> support person said that this was because Linux handles raw devices in a >> non-standard way, but that a new version of Linux to come out "soon" would >> fix this problem. Has anyone heard anything more specific about this? >> There are patches for Linux which enable raw devices but these are not in the stable Linux release only in the development version of the Linux kernel. These will eventually appear in the stable release possibly when the next stable release is produced. i.e. soon now. >> 2. Parts of the Admin Guide to IDS 9.2 say that performance with cooked >> files rather than raw devices can be worse by orders of magnitude. Has >> anyone found this to be true? >> I have heard of up to 20-30% gains but not orders of magnitude. Possibly this is because this part of the Informix manuals is quite old and this no longer applies on more modern UNIX versions. >> 3. Assuming that Linux does gain the ability to use raw devices with >> Informix, the Admin Guide says that chunks are max 2 Gb big and that offsets >> are max 2 Gb. My disks are 18 Gb. Am I correct in thinking that there >> would be no way to use them as Informix raw devices (except for the first 2 >> Gb) without using my SCSI card to RAID them and present them as a large >> number of 2 Gb logical drives? > Or use a logical Volume Manager. I believe an LVM support has been added to the latest development version of the kernel and again this will appear in the next stable kernel release. -- David Williams

On Sun, 16 Apr 2000 18:59:30 GMT, in comp.databases.informix Richard Puchalsky wrote: >I know this must be asked over and over, but I'm setting up Foundation 2000 >on Caldera Linux eServer 2.3 and I had some questions about raw devices: > >1. The machine notes say that Linux doesn't support raw devices. A tech >support person said that this was because Linux handles raw devices in a >non-standard way, but that a new version of Linux to come out "soon" would >fix this problem. Has anyone heard anything more specific about this? Linux 2.4 http://linuxtoday.com/stories/19955.html "One completely new feature in the Linux 2.4 kernel is the implementation of a "raw" I/O device. A raw device is one whose accesses are not handled through the caching layer, instead going right to the low-level device itself. A raw device could be used in cases where a sophisticated application wants complete control over how it does data caching and the expense of the usual cache is not wanted. Alternatively, a raw device could be used in data critical situations where we want to ensure that the data gets written to the disk immediately so that, in the event of a system failure, no data will be lost. Previous incarnations of this support were not fit for inclusion as they required literally doubling the number of device nodes so that every block device would also have a raw device node. (This is the implementation that many commercial UNIXes use.) The current implementation uses a pool of device nodes which can be associated with any arbitrary block device." "Linux 2.4 is almost ready" Considering that the develepment kernel is at ver 2.3.99-pre5 it is safe to say it will be ready Real Soon Now® How soon Foundation 2000 will support it is a whole different question. >2. Parts of the Admin Guide to IDS 9.2 say that performance with cooked >files rather than raw devices can be worse by orders of magnitude. Has >anyone found this to be true? It's hard to say, considering that there is no way to do a comparison, yet. >3. Assuming that Linux does gain the ability to use raw devices with >Informix, the Admin Guide says that chunks are max 2 Gb big and that offsets >are max 2 Gb. My disks are 18 Gb. Am I correct in thinking that there >would be no way to use them as Informix raw devices (except for the first 2 >Gb) without using my SCSI card to RAID them and present them as a large >number of 2 Gb logical drives? Also to be included in 2.4: "One huge area of improvement for Linux 2.4 has been the inclusion of the LVM (Logical Volume Manager) subsystem into the mainstream kernel. This is a system, standard in Enterprise-class UNIXes such as HP-UX and Tru64 UNIX (formerly Digital UNIX), that completely rethinks the way filesystems and volumes are managed. Without going into too many details, the LVM allows filesystems to span disks, be resized, and managed in a more flexible way than can be done using the current partition table schemes. Some of the features of the LVM subsystem can be replicated with the md (multiple device) driver or some userspace tools. However, the LVM subsystem offers this support in a (defacto) standards-compliant manner and in a way that will be at least somewhat familiar to users of commercial UNIXes." So you should be able to use the whole 18 gig disk or even several disks as a single raw device. I'm sure there must be some limit to size, but it's too early to know. -- «««««««««««««««««««««««»»»»»»»»»»»»»»»»»»»»»»»»»»» Milton B. Hewitt CAUCE Member - http://www.cauce.org Proud supporter of the Microsoft Boycott Campaign http://www.vcnet.com/bms/ «««««««««««««««««««««««»»»»»»»»»»»»»»»»»»»»»»»»»»»»

Thanks, everyone who posted on this. "Milton" <m.hewitt@mindspring.com> wrote (quoting an article): > Previous incarnations of this support were not fit for > inclusion as they required literally doubling the number of > device nodes so that every block device would also > have a raw device node. (This is the implementation that > many commercial UNIXes use.) And that's what SCO Unix uses, if I remember correctly. I never thought it was that bad a solution. It didn't have to be configured, at least. > "One huge area of improvement for Linux 2.4 has been > the inclusion of the LVM (Logical Volume Manager) > subsystem into the mainstream kernel. " I had forgotten that raw devices can exist on partitions, and that they don't literally need to represent an entire physical or logical device. So, as someone else pointed out, simple partitioning would work. LVMs are easier to manage, I'd guess.

In article <6sxgkAACfk+4EwMA@smooth1.demon.co.uk>, David Williams <djw@smooth1.demon.co.uk> wrote: [...] > There are patches for Linux which enable raw devices but these are > not in the stable Linux release only in the development version of > the Linux kernel. These will eventually appear in the stable release > possibly when the next stable release is produced. i.e. soon now. Currently: The latest stable version of the Linux kernel is: 2.2.14 The latest beta version of the Linux kernel is: 2.3.99-pre5 The latest prepatch (alpha) version appears to be: 2.3.99/6-3 Any speculation what 'soon now' is ? Thanks, Thanh Sent via Deja.com http://www.deja.com/ Before you buy.