Ulrich, According to what I read, whilst not directly affecting the physical disk, heads and cylinders do matter. It has something to do with the IO scheduler where it causes misalignemnt. It's a long story but it comes down to roughly twice the disk activity than is actually necessary. It seems the actual value of the number of heads and cylinders doesn't really matter, as long as it divisable by 2.
Besides that, I don't think I totally agree on your statement. Letting the IO scheduler taking the actual disk geometry into account, should give more performance. However, the fdisk default values are probably standard for disks these days. Nonetheless, a virtual server, unaware of the underlying hardware, does need these values to be set properly. On Dec 22, 1:18 pm, "Ulrich Windl" <ulrich.wi...@rz.uni-regensburg.de> wrote: > On 22 Dec 2008 at 2:19, Eric wrote: > > > > > > > > > Hello, > > > I'm going to setup a software raid over iSCSI. While I probably should > > ask my question to the raid people, my guess was someone here might > > have experience with this. > > > I'm going to use the following topology: > > > There will be 2 storage servers exporting targets. Other physical > > machines will initiate a target from each storage server to create a > > software raid (1). Virtual machines will use these raids as their > > disks. > > > Apart from the standard optimizations, there's one I haven't been able > > to find any information on. It is suggested that initiators, using the > > disks (in this case the virtualized machines) should use a head and > > cylinder count that is divisable by 2. Is this suggestion correct; > > does it (still) apply to iSCSI? > > Hi! > > I think since ZBR (Zone Bit Recording) the number of sectors per cylinder is > variable. thus it makes no sense for any higher-level disk software to try to > deal > with heads or cylinders. Since ATA (about 1990) only the controller on the > disk > knows the tracks, heads, and cylinders. The rest is just logic. Therefore SCSI > (nad now LBA) just uses logical block numbers. > > > > > Now for the actual question: I don't know exactly how linux software > > raid works internally, but it sounds like logic to me, that the > > software raid should be aware of the head and cylinder count as well. > > > So, when creating raid partitions on the targets, I should also modify > > the head and cylinder count on these. Is this a correct assumption and > > will software raid use the values advertised in the partition table? > > > Any answers or suggestions are appreciated. Thanks in advance. > > Only for MS-DOS compatibility you need C/H/S addressing. The rest doesn't care > AFAIK. > > Regards, > Ulrich > > > > > > > Kind regards, > > > Eric- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to email@example.com To unsubscribe from this group, send email to open-iscsi+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/open-iscsi -~----------~----~----~----~------~----~------~--~---