Messages in this thread | | | Date | Mon, 12 Jan 1998 07:54:29 +1100 | From | Richard Gooch <> | Subject | Re: scsi naming (was: devfs patch v3) |
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James Mastros writes: > On Sun, 11 Jan 1998, Richard Gooch wrote: > [...] > > However, this raises an issue that's been troubling me: how deep a > > directory structure should be implemented for SCSI discs? If you > > imagine a system with 8 SCSI hosts each with 8 SCSI channels (buses) > > with 8 drives per channel and 8 partitions per drive (let's leave the > > number of LUNs to a measly 1), that's 4096 directory entries in > > /dev/sd, which is painful to <ls>. Note that is a rather large system > > (someone with a huge disc farm), but the point is valid. > > So perhaps it would be better to have: > > /dev/sd/H/CciIlLpP > > > > But that's still 512 entries in each /dev/sd/*, so instead we could > > have: > > /dev/sd/H/C/iIlLpL > > > > which brings it down to 64. But then you can argue that you may have > > only 1 host with 8 channels, 8 targets per channel and 8 LUNs per > > target, each with 8 partitions. And on it goes. > > > > So, before I make any changes towards subdirectories in /dev, I want > > to get some kind of consensus (at least from those not implacably > > opposed to devfs) as to how deep these directory structures should go. > > I should think that we want them as deep as we can go. After-all, there is > an overhead of one dentry and one inode in memory for each one, but we only > have that overhead for directories that we acatually have... So my > suggested directory structure looks like: > > SCSI/ > c/ > controller > b/ > bus > id/ > id > lun/ > lun > partition > > (where the direcories c, b, id, and lun (and the node partition) are > numbers, and the nodes controller, bus, id, and lun are nodes for ioctls > that effect the entire controller, bus, id, or lun). Indeed, perhaps the > partitions should be directories that mirror the partition structure on-disk > (so exteneded dos partitions would be directories.) Note that my scheme > dosn't diferincate between hard-drives, tape-drives, cdrom-drives, and > generics -- I think that they should be merged: does anybody know why they > weren't in the first place? (I don't have any SCSI devices, so I don't > really know.)
Firstly, I think the entire SCSI disc should be a file: reading and writing directories seems not to be the done thing. I note that ext2 disallows reading of directories, and the VFS disallows opening of directories in write mode.
Secondly, take drives don't have partitions. I dunno about CD-ROMS.
Thirdly, I think you *want* to differentiate between hard discs and tape drives, at a fairly high level. "What tape drives do I have?" Looking for one tape driver amongst 100 SCSI discs is like looking for a needle in a haystack.
Regards,
Richard....
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