Messages in this thread | | | From | Jakub Jelinek <> | Subject | Re: Poor device management | Date | Tue, 19 May 1998 10:29:16 +0200 (MET DST) |
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> > Hi, > > I would like to address the topic of naming of devices. Currently, we > have two serious problems: > > 1. It appears that Linux can support a maximum of 16 SCSI hard drives > per system, according to devices.txt. > > This is a serious issue as we would like to have more than that on > some machines but the OS does not appear to support that. The > allocated block of device numbers appears to have no support for more.
This is not true. This stuff is currently coded in VGER CVS tree and I hope will get into Linus' tree soon (as Linux is not very usable for mid to large servers without it). There was a couple of problems we had to solve, but at the moment it runs just fine.
[root@1000e /root]# cat /proc/mdstat Personalities : [2 raid0] read_ahead 128 sectors md0 : active raid0 sdk1 sdl1 sdm1 sdn1 16757248 blocks 32k chunks md1 : active raid0 sdp1 sdq1 sdr1 sdu1 16757248 blocks 32k chunks md2 : active raid0 sdv1 sdw1 sdx1 sdz1 16757248 blocks 32k chunks md3 : active raid0 sdaa1 sdab1 sdac1 sdai1 16757248 blocks 32k chunks md4 : active raid0 sdaj1 sdak1 sdal1 sdag1 16757248 blocks 32k chunks md5 : active raid0 sdo1 sds1 sdt1 sdy1 sdad1 sdam1 6153792 blocks 32k chunks md6 : active raid0 sdc1 sdd1 sde1 sdf1 16781568 blocks 32k chunks md7 : active raid0 sdh1 sdi1 sdj1 8842632 blocks 8k chunks md8 : active raid0 sdae1 sdaf1 sdah1 sdg1 16763328 blocks 32k chunks md9 : inactive md10 : inactive md11 : inactive md12 : inactive md13 : inactive md14 : inactive md15 : inactive
> > 2. Device numbers can change between boots or even during operation. > > This is because the device numbers (and thus, /dev entries) are > allocated in sequential order. Thus, for instance, if my Jaz drive > (SCSI ID 4) is turned off but my scanner (ID 5) is on, the scanner > gets a particular device assigned to it. However, it the Jaz drive is > on when the system boots, the Jaz gets that ID and the scanner gets > something different. > > It would, therefore, be highly advisable to go to something akin to > Solaris -- the /dev entries specify controller, target, and LUN > expliticly. This will remove a lot of confusion especially > surrounding the sg devices and eliminate the problem of drifting > device entries.
There is devfs filesystem (Richard Gooch posts announces about it every couple of days), which solves this issue. I think it would be a very good idea to include that into 2.2 kernel - it is just another filesystem and quite a bit tested, so it should not bring instabilities into the kernel. But it really makes system administration easier. On the above server, if I insert a tray with some more disks that get new sdc-sdi, for instance, I have to rename a lot of disks in my /etc/mdtab making script and get it right, otherwise I may loose my data, when first fsck hits some disks. The script is needed, as when you change disk names, the mdcreate magic changes as well. Now, with devfs there is no need for such script - the names stay the same.
Cheers, Jakub ___________________________________________________________________ Jakub Jelinek | jj@sunsite.mff.cuni.cz | http://sunsite.mff.cuni.cz Administrator of SunSITE Czech Republic, MFF, Charles University ___________________________________________________________________ Ultralinux - first 64bit OS to take full power of the UltraSparc Linux version 2.1.102 on a sparc64 machine (498.80 BogoMips). ___________________________________________________________________
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