On Fri, 2007-08-10 at 09:24 -0400, Robert P. J. Day wrote: > On Fri, 10 Aug 2007, Timothy Murphy wrote: > > > Rick Stevens wrote: > > > > > Well, the "x" in your example can take the RE form "[a-z]+". For > > > example, we have some storage arrays with, oh, 130 LUNs on them. They > > > appear as /dev/sda[1-15] through /dev/sdiv[1-15] > > > > But you won't get this with the standard Fedora installation, which > > I assume is what people are talking about. You will be told you have > > disks /dev/sda and /dev/sdb, or whatever, and asked how you want to > > partition them. > > not to harp on this, but can someone confirm that, with standard hard > disks and partitioning, the limits are: > > 1) 4 primary partitions > 2) only one of which can be extended > 3) that extended partition can hold up to 12 logical partitions (this > limit is different from IDE to SCSI, as i recall) > > in any event, it's simply not true that you can have an unbounded > number of logical partitions on a single drive, unless something's > changed drastically lately. To answer many of the queries to my posting: 1. When I referred to a "storage array", I am referring to a number of SAN systems we have here, some based on EMC CX3/20s and some on Hitachi 9585s. These SAN systems have large numbers of individual spindles bunched together as various types of RAIDs (RAID5, RAID10, etc.). These RAID groups are presented by the SAN controller over fiberchannel HBAs to the host machines and appear as if they were separate physical disks to Linux. In one case, these RAID groups appear as SCSI disks /dev/sda through /dev/sdiv. We then use these devices as PVs under LVM and stitch them together as needed. 2. SCSI does not limit LUNs to 16. In reality, LUNs are identified by a 64-bit number that can be broken down into several different models. In the simplest model, the LUN is represented by an 8-bit number, giving 256 LUNs. Other mechanisms are possible. You need to look at the SAM-2 specification, specifically section 4.9. It can be a bit mind-bending to read. 3. Again, the 4 primary partition thing is an artifact from the PC BIOS. There are systems that use a totally different partitioning scheme. The disks themselves don't give a toss. 4. The virtual partitions inside a primary extended partition are not limited to 24 or whatever someone said earlier...that's an artifact of the DOS/Windows limiting of hard drive letters to c: through z:. There's nothing in the spec that says 24's the limit. ---------------------------------------------------------------------- - Rick Stevens, Principal Engineer rstevens@xxxxxxxxxxxx - - CDN Systems, Internap, Inc. http://www.internap.com - - - - Brain: The organ with which we think that we think. - ----------------------------------------------------------------------
