Re: Newbie gmirror questions
On Sunday 17 January 2010, Matthew Seaman wrote: However, one of the really amazingly brilliant things about geom is that just about any disk / storage related thing can be a geom provider, and geom constructs will nest very happily. Here's a howto for setting up gmirror across a pair of slices: http://people.freebsd.org/~rse/mirror/ Thanks for all the advice, my mirrors are now up and running on 2 of the 4 slices without any problems. But just one last dumb question. Does gmirror consider one of the consumers to act as a master for the pair? The reason I ask is that earlier today I needed to disconnect a few cables inside the PC to get better access to a bit of internal hardware and then realised that although I knew which two SATA connectors to use for the mirror drives I'd failed to make a note of which order the drives were connected. I felt about 75% sure I'd paired them up the same way as before so went ahead, everything started up OK and gmirror status shows the status for both mirrors as COMPLETE. Now I'm wondering if I was just lucky or if it just doesn't matter if the order of mirror consumers is interchanged after creation. -- Mike Clarke ___ 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: Newbie gmirror questions
Does gmirror consider one of the consumers to act as a master for the pair? No. The order doesn't matter. You could take out your hard drives and shuffle them like cards and it wouldn't matter. All metadata is stored in the last sector of the drives themselves. Cable order is irrelevant. -Modulok- On 2/5/10, Mike Clarke jmc-freeb...@milibyte.co.uk wrote: On Sunday 17 January 2010, Matthew Seaman wrote: However, one of the really amazingly brilliant things about geom is that just about any disk / storage related thing can be a geom provider, and geom constructs will nest very happily. Here's a howto for setting up gmirror across a pair of slices: http://people.freebsd.org/~rse/mirror/ Thanks for all the advice, my mirrors are now up and running on 2 of the 4 slices without any problems. But just one last dumb question. Does gmirror consider one of the consumers to act as a master for the pair? The reason I ask is that earlier today I needed to disconnect a few cables inside the PC to get better access to a bit of internal hardware and then realised that although I knew which two SATA connectors to use for the mirror drives I'd failed to make a note of which order the drives were connected. I felt about 75% sure I'd paired them up the same way as before so went ahead, everything started up OK and gmirror status shows the status for both mirrors as COMPLETE. Now I'm wondering if I was just lucky or if it just doesn't matter if the order of mirror consumers is interchanged after creation. -- Mike Clarke ___ 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: Newbie gmirror questions
On Sunday 17 January 2010, Matthew Seaman wrote: However, one of the really amazingly brilliant things about geom is that just about any disk / storage related thing can be a geom provider, and geom constructs will nest very happily. Here's a howto for setting up gmirror across a pair of slices: http://people.freebsd.org/~rse/mirror/ That's a very interesting article. Since I'll be able to configure the mirror on the new drives before installing any software my approach can be a bit simpler. In the example he's using a single partition for the whole disk but reduces the size if the partition by one block so that the mirror's meta data doesn't get misinterpreted as whole disk meta data. Since I anticipate using only the first 2 partitions for a couple of mirrors and using the rest of the disk as plain partitions then I don't think I need to do this but might it still be a good idea to reduce the last partition by one block anyway in case my usage changes in the future? -- Mike Clarke ___ 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: Newbie gmirror questions
On Saturday 16 January 2010, Pieter de Goeje wrote: On Saturday 16 January 2010 00:34:52 Mike Clarke wrote: I'm about to upgrade to more disk space and I'm tempted use this as an opportunity to get two disks and implement gmirror. Before I go ahead there's a few aspects of mirroring I'm not sure about and would appreciate some advice. I'm using grub for multi booting. Does this introduce any problems if I want to boot into Windows or Linux on one of the other partitions? Gmirror stores the metadata at the last sector of each disk. So this shouldn't be a problem. But other operating systems might overwrite this data if you're not careful during the paritioning. I'll make sure that the last stripe on the disk isn't used by any alien OS then. Actually I was more concerned about what happens when I boot into another OS like Windows or Linux on one of the spare slices - I'm assuming that I have to apply gmirror to the whole disk rather than just selected slices? My main reason for multibooting with grub is to have a spare slice where I can install a spare copy of FreeBSD. I find this very useful when I do any major upgrade (like trying out your suggestion of going to 8-STABLE) because I can copy the current system onto the spare slice and use that to apply the upgrades, if I hit any major problems I can easily revert to booting the original slice until I figure out how to fix the problem. I'm assuming that using gmirror won't prevent me from doing this. If I boot into an OS which isn't aware of gmirror, such as Windows, then I assume it will just run normally if I point grub to the appropriate slice on the primary drive. Next time I boot into FreeBSD then I expect gmirror will recognise that the second drive is out of sync with the primary and update it in the background. Perhaps this might hit performance for a while but on the other hand it provides me with a certain amount of backup if the Windows system trashes itself because I could try to restore it from the copy on the second drive before attempting to reboot FreeBSD. I assume the same logic would also apply to running Linux on one of the slices, although Linux has software mirror capability it appears to be totally different from gmirror so I expect it's a case of running that non-mirrored too. If this approach isn't wise then I expect I'll need to keep a spare non-mirrored disk for the other systems. I don't expect to need to boot into Windows or Linux very often. Now that I've upgraded from FreeBSD 6.4 to 8.0 I'm able to make use of virtualbox for this sort of thing which is generally much more convenient but I'd like to keep the ability to run them natively should the need arise. -- Mike Clarke ___ 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: Newbie gmirror questions
Mike Clarke wrote: Actually I was more concerned about what happens when I boot into another OS like Windows or Linux on one of the spare slices - I'm assuming that I have to apply gmirror to the whole disk rather than just selected slices? You can't do this. gmirror is FreeBSD specific, and other OSes can't deal with it. You can take your two drives, partition them (fdisk) and then create a gmirror across the slices you assign to FreeBSD. Similarly you could set up md to mirror the slice(s) used for Linux. As far as I know, Windows doesn't come with OS level mirroring software -- it can use hostraid[*], or I believe there are some commercial solutions you can purchase. Or just treat your Windows partitions as two separate drives, and live without resilience for that OS. As far as booting the system goes, Grub should be able to boot each OS from either mirror as if it was a plain installation on a single drive. Wilder suggestions would be to install Linux, Open Solaris or NetBSD as a Xen dom0, and then install your other OSes as domU guests. In this case, you'ld mirror the storage within the dom0 instance and export a device to each of the client OSes. [Open Solaris particularly interesting for this purpose, as you could use ZFS.] This is substantially more complex to set up than your current plan, but does have the very handy advantage that you can run all of your OSes simultaneously. Cheers, Matthew [*] FreeBSD can use this too -- the disks appear as an ar device (see ata(4)) -- and presumably so can Linux, but I can't confirm that. Hostraid is generally second best to OS based RAIDs. Apart from anything else, you tend to have to bring the system down to the BIOS level to do anything to the RAIDs. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW signature.asc Description: OpenPGP digital signature
Re: Newbie gmirror questions
On Sunday 17 January 2010, Matthew Seaman wrote: Mike Clarke wrote: Actually I was more concerned about what happens when I boot into another OS like Windows or Linux on one of the spare slices - I'm assuming that I have to apply gmirror to the whole disk rather than just selected slices? You can't do this. gmirror is FreeBSD specific, and other OSes can't deal with it. You can take your two drives, partition them (fdisk) and then create a gmirror across the slices you assign to FreeBSD. This will make things a lot easier for me. I think all the examples of gmirror I've seen used things like /dev/da0 as the provider in label commands so I assumed that I had to use the whole physical disk but if I can mirror individual slices then I have much more flexibility. My motherboard has a UDMA133 controller for ata0 ata1 (which I don't use) and 2 SATA controllers for ata2 to ata5 so with my 2 SATA drives spread between the controllers on channels 2 4 I could have something like /dev/mirror/gm1 provided by /dev/ad2s1 /dev/ad4s1 and /dev/mirror/gm2 provided by /dev/ad2s2 /dev/ad4s2 for a couple of FreeBSD systems. That will leave me with 2 spare slices on each drive for other purposes. Any Windows or Linux stuff I put on tends to be mainly experimental and less long term than my FreeBSD system so don't really need the resilience of being mirrored. -- Mike Clarke ___ 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: Newbie gmirror questions
Mike Clarke wrote:
On Sunday 17 January 2010, Matthew Seaman wrote:
Mike Clarke wrote:
Actually I was more concerned about what happens when I boot into
another OS like Windows or Linux on one of the spare slices - I'm
assuming that I have to apply gmirror to the whole disk rather than
just selected slices?
You can't do this. gmirror is FreeBSD specific, and other OSes can't
deal with it. You can take your two drives, partition them (fdisk)
and then create a gmirror across the slices you assign to FreeBSD.
This will make things a lot easier for me. I think all the examples of
gmirror I've seen used things like /dev/da0 as the provider in label
commands so I assumed that I had to use the whole physical disk but if
I can mirror individual slices then I have much more flexibility.
My motherboard has a UDMA133 controller for ata0 ata1 (which I don't
use) and 2 SATA controllers for ata2 to ata5 so with my 2 SATA drives
spread between the controllers on channels 2 4 I could have something
like /dev/mirror/gm1 provided by /dev/ad2s1 /dev/ad4s1
and /dev/mirror/gm2 provided by /dev/ad2s2 /dev/ad4s2 for a couple of
FreeBSD systems. That will leave me with 2 spare slices on each drive
for other purposes. Any Windows or Linux stuff I put on tends to be
mainly experimental and less long term than my FreeBSD system so don't
really need the resilience of being mirrored.
Yes -- there's an On-Lamp article by Dru Lavigne that has been particularly
influential, and gmirror'ing whole disks is the best way forwards for the
vast majority of cases where you've a server dedicated to one OS.
However, one of the really amazingly brilliant things about geom is that
just about any disk / storage related thing can be a geom provider, and
geom constructs will nest very happily. Here's a howto for setting up
gmirror across a pair of slices:
http://people.freebsd.org/~rse/mirror/
It's fairly old now, but the essentials are still correct. The one thing
that has changed in the intervening time is what is the best algorithm
to use for the gmirror. Up until the release of 8.0, 'round-robin' was
virtually always the right choice, but nowadays 'load' is preferred.
All that means, is change the following line in rse's article from:
gmirror label -v -n -b round-robin ${gm} /dev/${d2}s1
to
gmirror label -v -n -b load ${gm} /dev/${d2}s1
Cheers,
Matthew
--
Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
Kent, CT11 9PW
signature.asc
Description: OpenPGP digital signature
Re: Newbie gmirror questions
On 17.01.2010 19:18, Matthew Seaman wrote: Mike Clarke wrote: Actually I was more concerned about what happens when I boot into another OS like Windows or Linux on one of the spare slices - I'm assuming that I have to apply gmirror to the whole disk rather than just selected slices? You can't do this. gmirror is FreeBSD specific, and other OSes can't deal with it. You can take your two drives, partition them (fdisk) and then create a gmirror across the slices you assign to FreeBSD. Similarly you could set up md to mirror the slice(s) used for Linux. As far as I know, Windows doesn't come with OS level mirroring software -- it can use hostraid[*], or I believe there are some commercial solutions you can purchase. Or just treat your Windows partitions as two separate drives, and live without resilience for that OS. I can correct you here. XP Pro and later do know about 'dynamic' disks and they can make mirrors from them. Booting from such disks is a kind pain in the ass but it works for RAID0, RAID1, RAID0+1 and RAID5 setup. I can be wrong, I'm not a Win-fan, I just do know this exists. You can find details here: http://support.microsoft.com/default.aspx/kb/816307 -- Sphinx of black quartz judge my vow. ___ 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: Newbie gmirror questions
On Saturday 16 January 2010 00:34:52 Mike Clarke wrote: I'm about to upgrade to more disk space and I'm tempted use this as an opportunity to get two disks and implement gmirror. Before I go ahead there's a few aspects of mirroring I'm not sure about and would appreciate some advice. I'm using grub for multi booting. Does this introduce any problems if I want to boot into Windows or Linux on one of the other partitions? Gmirror stores the metadata at the last sector of each disk. So this shouldn't be a problem. But other operating systems might overwrite this data if you're not careful during the paritioning. The gmirror manpage describes the procedure for handling kernel dumps using the prefer balance algorithm in the early stages of booting and then switching to round-robin in the /etc/rc.local script. It then goes on to say that If on the next boot a component with a higher priority will be available, the prefer algorithm will choose to read from it and savecore(8) will find nothing. Does this only arise if I've made some change to the configuration of the mirror between the dump and the reboot or is there some instances when the priority automatically changes? Priority never changes automatically. Some of the articles I've read about gmirror suggest setting the balance to round-robin while others just leave this at the default setting of split. Am I right in assuming that round-robin would give better performance, and does it make much noticeable difference in real terms. In particular am I likely to see a reduction in performance using gmirror compared with what I would get with just a normal single disk. Assuming you have two or more regular HDDs, I can recommend updating to 8-STABLE and using the load algorithm. It has had some major improvements lately, and is now the default. It should give equal or better read performance in comparison to a single disk in all cases. The performance of split and round-robin is very dependent on the access patterns and stripe size (for split). Finally, recent articles say to set kern.geom.debugflags to 17 when creating a mirror on a mounted drive while older articles say to set it to 16. Although I'll probably be creating the mirror on my disks before copying my system onto them so I don't really need to worry about setting this flag but I'm curious to know the difference between using the two values. The sysctl is a bitfield, so 17 (0x11) enables some extra stuff compared to 16 (0x10). See geom(4), section DIAGNOSTICS for more details. -- Pieter de Goeje ___ 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
