Re: 8GB limitation in RAID
"Thanh" <tqma@my-deja.com> wrote in message news:8s4rui$ou8$1@nnrp1.deja.com... > Anyone knows if there has even been an 8GB addressing limitation in > some SCSI RAID controllers ? Or this is just a bad information. An addressing limitation I doubt (I have used disks this large on controllers made many years ago), however many controllers that support INT13 booting via the BIOS, will have the normal limit for INT13 at 8GB. In fact with OS's that still only 'understand' INT13 (not the extended version), there will _still_ be an 8GB limit during boot, even with 'brand new' controllers (NT for instance still has this limit). Best Wishes
In article <971384857.12042.0.nnrp-02.9e988e54@news.demon.co.uk>, "Roger Hamlett" <roger@ttelmah.demon.co.uk> wrote: > > "Thanh" <tqma@my-deja.com> wrote in message > news:8s4rui$ou8$1@nnrp1.deja.com... > > Anyone knows if there has even been an 8GB addressing limitation in > > some SCSI RAID controllers ? Or this is just a bad information. > An addressing limitation I doubt (I have used disks this large on > controllers made many years ago), however many controllers that support > INT13 booting via the BIOS, will have the normal limit for INT13 at 8GB. > In fact with OS's that still only 'understand' INT13 (not the extended > version), there will _still_ be an 8GB limit during boot, even with 'brand > new' controllers (NT for instance still has this limit). So... can I say that the limitation, if any, is in the OS and not in the controller (that supports both INT13 and extended version) ? Thanh Sent via Deja.com http://www.deja.com/ Before you buy.
"Thanh" <tqma@my-deja.com> wrote in message news:8s5ds3$9bs$1@nnrp1.deja.com... > In article <971384857.12042.0.nnrp-02.9e988e54@news.demon.co.uk>, > "Roger Hamlett" <roger@ttelmah.demon.co.uk> wrote: > > > > "Thanh" <tqma@my-deja.com> wrote in message > > news:8s4rui$ou8$1@nnrp1.deja.com... > > > Anyone knows if there has even been an 8GB addressing limitation in > > > some SCSI RAID controllers ? Or this is just a bad information. > > An addressing limitation I doubt (I have used disks this large on > > controllers made many years ago), however many controllers that > support > > INT13 booting via the BIOS, will have the normal limit for INT13 at > 8GB. > > In fact with OS's that still only 'understand' INT13 (not the extended > > version), there will _still_ be an 8GB limit during boot, even > with 'brand > > new' controllers (NT for instance still has this limit). > > So... can I say that the limitation, if any, is in the OS and not > in the controller (that supports both INT13 and extended version) ? Well, it could be in several places!. The first is with INT13 (obvious), the second is with the drivers, and the third is with the OS itself. You then have the 'interaction' of all these effects. Let me give you an example (not with a RAID controller). If you look at the really early ISA SCSI cards (15xx family). The first variants, had a BIOS that only supported up to 1GB on boot. Yet if you loaded an OS like Unix, these same cards could happily support drives several GB in size. However the drivers supplied with the first versions of SCO Unix, themselves had a limit that caused seperately a problem when drives went over 8GB. So three 'different' size limits, according to the software used. You have the question of the OS size limits, then what address range is supported by the drivers, then any 'hardware' limits in the ability to put this address range on the SCSI bus, and then any BIOS limits. Now most RAID controllers use proprietary SCSI controller chips that do not have any limits at this point. You then have the controller chip used (and it's firmware) on the board itself. This could easily have a limit, but should be fixable by upgradeing the firmware. Also unless the card is incredibly old, this is unlikely, since even quite early RAID controllers had to be able to handle GB 'virtual' drives (even with 512MB drives, on a single channel 'narrow' SCSI controller, 3GB would be easy, and the manuacturers would be unlikely to not foresee the small expansion needed to read 8GB). The problem is that you can get an OS, that stores it's 'address' (whether it be sector, track, LBA etc.), in one format, then a different format used on the controller. Depending on how the driver handles the translation between these formats, you can get yet more 'limits' appearing (this was what happened with the SCO drivers). The 'INT13' limit, is the commonest one, and as I said, is _still_ applicable even with modern controllers. All the other likely limits, are fixable be software/firmware upgrades. A 'hardware' limit at 8GB, is very improbable with SCSI. Why not just post the details of the controller?. If it is any of the well known makes, full details should be available, and we can get away from "maybe's"... Best Wishes