Re: Should root partition be first partition?
b. f. wrote: On 2/8/10, Jerry McAllister jerr...@msu.edu wrote: On Mon, Feb 08, 2010 at 02:37:30PM -0500, b. f. wrote: [snip] If you're laying out a new disk, you may as well take a few minutes and get the most out of it, even if you're not going to invest in a lot of new hardware. The system nowdays does all that figuring for you and manages boundaries reasonably. jerry That does not seem to be the conclusion of those who contributed to the thread I cited, although reasonably is open to interpretation. This will become more critical with the upcoming transition from 512K to 4K sector size. Indeed, I believe it was initial investigations for implementation of this and/with comparison against other OS methods. The large performance differences witnessed led to a deeper, more retrospective look at current approaches based on 512K sectors as well. -Mike ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Should root partition be first partition?
At 8:09 AM -0600 2/8/10, Peter Steele wrote: I've set up a system with gpart and have the swap partition first followed by root, var, and so on. This works fine but I've seen documents that always have root first, then swap. Is there any reason that root should be the first partition or can it follow swap space? In the world of MBR partitioning, there is some situation where it's important that the root partition be 'a'. Unfortunately, I don't remember what it was. Probably something having to do with the boot loader. I do remember running into it once when I had the root partition as 'd' by mistake. But that was several years ago, so I don't remember the details. In any case, I would not expect the same problems to come up once you're using gpart partitioning. -- Garance Alistair Drosehn= g...@gilead.netel.rpi.edu Senior Systems Programmer or g...@freebsd.org Rensselaer Polytechnic Instituteor dro...@rpi.edu ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Should root partition be first partition?
I've set up a system with gpart and have the swap partition first followed by root, var, and so on. This works fine but I've seen documents that always have root first, then swap. Is there any reason that root should be the first partition or can it follow swap space? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Should root partition be first partition?
On Mon, Feb 08, 2010 at 08:09:48AM -0600, Peter Steele wrote: I've set up a system with gpart and have the swap partition first followed by root, var, and so on. This works fine but I've seen documents that always have root first, then swap. Is there any reason that root should be the first partition or can it follow swap space? It should work, but there are so many things that might assume to have / (root) as the first partition on a bootable drive that maybe it is best to just stick with that convention. jerry ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Should root partition be first partition?
On 08/02/2010 14:09, Peter Steele wrote: I've set up a system with gpart and have the swap partition first followed by root, var, and so on. This works fine but I've seen documents that always have root first, then swap. Is there any reason that root should be the first partition or can it follow swap space? The root partition should always be the 'a' partition, but it doesn't have to be the first in physical order on the disk (ie. starting at cylinder 0). So long as partitions don't overlap (with the historical exception of the 'c' partition, which should cover the whole drive) you can put them in any order and starting at any offset. You can even leave gaps between partitions if you want, but that is pretty crazy since it just wastes some of the available space. There have been quite a lot of recommendations on how to lay out a disk for best performance, based on the observation that disk access times vary depending on how far away the data is from the spindle, and the expected usage patterns for the partition. Like any such advice, it has tended to become less valid over time. Modern disks really don't have any physical meaning to the Cylinder/Head/Sector style addressing schemes[*] nowadays -- and you're pretty much bound to be using LBA style addressing anyhow. Also, machines nowadays have so much RAM that (a) swap is hardly ever used and (b) access to popular files is frequently answered out of VM caches rathe than needing disk IO. If your application is so demanding that you really need to squeeze out the last drop of IO performance, then you're much better off investing in fast SAS drives, a decent HW RAID controller with BBU and extra RAM. Otherwise, don't sweat it. Lay out the disks in a way that makes sense to you, and carry on with your life... Cheers, Matthew [*] But this still pops up in sysinstall, at the cost of much bewilderment for the uninitiated. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard, Flat 3 Black Earth Consulting Ramsgate Kent, CT11 9PW Free and Open Source Solutions Tel: +44 (0)1843 580647 signature.asc Description: OpenPGP digital signature
RE: Should root partition be first partition?
The root partition should always be the 'a' partition, but it doesn't have to be the first in physical order on the disk (ie. starting at cylinder 0). So long as partitions don't overlap (with the historical exception of the 'c' partition, which should cover the whole drive) you can put them in any order and starting at any offset. You can even leave gaps between partitions if you want, but that is pretty crazy since it just wastes some of the available space. I should clarify that I am using GPT partitions, not MBR, so in fact there is no 'a' partition and in fact no bsd label at all. My partitioning looks like this: # gpart show ad4 = 34 490234685 ad4 GPT (234G) 34 161 freebsd-boot (8.0K) 50 671088642 freebsd-swap (32G) 67108914 671088643 freebsd-swap (32G) 134217778 104857604 freebsd-ufs (5.0G) 144703538 251658245 freebsd-ufs (12G) 16986936257925576 freebsd-ufs (2.8G) 175661919 2831155207 freebsd-ufs (135G) 458777439 314572808 freebsd-ufs (15G) Partition 4 (ad4p4) is the root partition. This works fine, but I was just wondering why I've seen layouts with root first, then swap, then var, etc. The only problem I've had is that I cannot find a way to tell the boot loader to boot from an alternate drive since it seems to expect MBR partitioning when using a reference such as 4:ad(4,a)/boot/loader. That's a separate issue though. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Should root partition be first partition?
You can even leave gaps between partitions if you want, but that is pretty crazy since it just wastes some of the available space. There have been quite a lot of recommendations on how to lay out a disk for best performance, based on the observation that disk access times vary depending on how far away the data is from the spindle, and the expected usage patterns for the partition. Like any such advice, it has tended to become less valid over time. Modern disks really don't have any physical meaning to the Cylinder/Head/Sector style addressing schemes[*] nowadays -- and you're pretty much bound to be using LBA style addressing anyhow. Also, machines nowadays have so much RAM that (a) swap is hardly ever used and (b) access to popular files is frequently answered out of VM caches rathe than needing disk IO. Layout is still important, and leaving some blank space may not be so crazy. Here I'm thinking not so much of ordering (although one would probably be best served by the recommended default ordering), but of alignment, size, raid/stripe/concat configuration, and file system block and fragment size selection. Witness the (as much as tenfold) performance difference from simple changes, highlighted in the recent thread entitled 'File system blocks alignment' on freebsd-arch@ during December 2009 - January 2010, beginning with: http://lists.freebsd.org/pipermail/freebsd-arch/2009-December/009770.html If you're laying out a new disk, you may as well take a few minutes and get the most out of it, even if you're not going to invest in a lot of new hardware. b. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Should root partition be first partition?
On Mon, Feb 08, 2010 at 02:37:30PM -0500, b. f. wrote: You can even leave gaps between partitions if you want, but that is pretty crazy since it just wastes some of the available space. There have been quite a lot of recommendations on how to lay out a disk for best performance, based on the observation that disk access times vary depending on how far away the data is from the spindle, and the expected usage patterns for the partition. Like any such advice, it has tended to become less valid over time. Modern disks really don't have any physical meaning to the Cylinder/Head/Sector style addressing schemes[*] nowadays -- and you're pretty much bound to be using LBA style addressing anyhow. Also, machines nowadays have so much RAM that (a) swap is hardly ever used and (b) access to popular files is frequently answered out of VM caches rathe than needing disk IO. Layout is still important, and leaving some blank space may not be so crazy. Here I'm thinking not so much of ordering (although one would probably be best served by the recommended default ordering), but of alignment, size, raid/stripe/concat configuration, and file system block and fragment size selection. Witness the (as much as tenfold) performance difference from simple changes, highlighted in the recent thread entitled 'File system blocks alignment' on freebsd-arch@ during December 2009 - January 2010, beginning with: http://lists.freebsd.org/pipermail/freebsd-arch/2009-December/009770.html If you're laying out a new disk, you may as well take a few minutes and get the most out of it, even if you're not going to invest in a lot of new hardware. The system nowdays does all that figuring for you and manages boundaries reasonably. jerry b. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Should root partition be first partition?
On 2/8/10, Jerry McAllister jerr...@msu.edu wrote: On Mon, Feb 08, 2010 at 02:37:30PM -0500, b. f. wrote: You can even leave gaps between partitions if you want, but that is pretty crazy since it just wastes some of the available space. There have been quite a lot of recommendations on how to lay out a disk for best performance, based on the observation that disk access times vary depending on how far away the data is from the spindle, and the expected usage patterns for the partition. Like any such advice, it has tended to become less valid over time. Modern disks really don't have any physical meaning to the Cylinder/Head/Sector style addressing schemes[*] nowadays -- and you're pretty much bound to be using LBA style addressing anyhow. Also, machines nowadays have so much RAM that (a) swap is hardly ever used and (b) access to popular files is frequently answered out of VM caches rathe than needing disk IO. Layout is still important, and leaving some blank space may not be so crazy. Here I'm thinking not so much of ordering (although one would probably be best served by the recommended default ordering), but of alignment, size, raid/stripe/concat configuration, and file system block and fragment size selection. Witness the (as much as tenfold) performance difference from simple changes, highlighted in the recent thread entitled 'File system blocks alignment' on freebsd-arch@ during December 2009 - January 2010, beginning with: http://lists.freebsd.org/pipermail/freebsd-arch/2009-December/009770.html If you're laying out a new disk, you may as well take a few minutes and get the most out of it, even if you're not going to invest in a lot of new hardware. The system nowdays does all that figuring for you and manages boundaries reasonably. jerry That does not seem to be the conclusion of those who contributed to the thread I cited, although reasonably is open to interpretation. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Should root partition be first partition?
On Monday 08 February 2010 14:09:48 Peter Steele wrote: I've set up a system with gpart and have the swap partition first followed by root, var, and so on. This works fine but I've seen documents that always have root first, then swap. Is there any reason that root should be the first partition or can it follow swap space? It may partly be historical: old PCs couldn't boot from past 504MB due to the 1023 cylinder limitation so /boot had to be first on the disk. -- Bruce Cran ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
