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FizzyWidget
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PostPosted: Thu Oct 04, 2012 9:08 am    Post subject: Installing to raid0+1 and swap? Reply with quote

Finally have the time to change file server from Windows to Gentoo but have a few questions about raid and swap.

This is the layout I have come up with, nice and simple

100m /boot

Code:
mdadm --create --verbose /dev/md0 --level=1 --raid-devices=4 /dev/sd[abcd]1



???? /swap - see below


Code:
mdadm --create --verbose /dev/md1 --level=0 --raid-devices=4 /dev/sd[abcd]2



15G /


Code:
mdadm --create --verbose /dev/md2 --level=01 --raid-devices=4 /dev/sd[abcd]3



rest of the drives for /home


Code:
mdadm --create --verbose /dev/md3 --level=01 --raid-devices=4 /dev/sd[abcd]4



Is that the right way to make Raid0+1 arrays? I have looked at the Gentoo docs but they just tend to give Raid 0 1 5 examples.

As for swap how much do you need for swap? I normally use the 1.5 X ram method, but is this still the way to do it ? There is 4G of ram in there atm so i would normally put the swap file at 6G
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NeddySeagoon
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PostPosted: Thu Oct 04, 2012 6:11 pm    Post subject: Reply with quote

Dark Foo,

If you need more than 512Mb swap on a desktop, you are doing something wrong. Your only excuse is hibernate to swap when you need swap>=RAM.

Why would you make a rais0 swap?
The kernel does something similar if you give it four swap partitions at the same priority. Losing swap is the same as giiving some of your applications a lobotomy. You will noyt like the result.
If you will use raid levels that provide redundency, whu skipm on swap.

If you will use grub1 on /boot, you must use version 0.90 raid metadata
If you want raid auto assembly you must use version 0.90 raid metadata too.

I think the level you want is 10 rather than 01.
Code:
man mdadm
talks about RAID10.

Why raid 10 and not raid5?
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FizzyWidget
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PostPosted: Thu Oct 04, 2012 6:18 pm    Post subject: Reply with quote

after a lot of research it seems raid10 gives better performance and redundancy over raid5.

So other than the swap amount my approach is good?

I went for raid0 on swap for performance and seeing that swap is wiped on boot (or so i believe) what is the point in having it as raid10, I could make all of them raid10, i will be using grub2 as i mainly use amd64, to be honest i could make 2 raids one for boot and the other for everything else ,just needed a bit of information to be Forewarned is to be forearmed :D
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PostPosted: Thu Oct 04, 2012 7:04 pm    Post subject: Reply with quote

Dark Foo,

Raid10 protects against the loss of a single drive and the loss of some combinations of two drives.
Raid0 on swap will kill any process using a spindle that fails. Don't expect your system to stay up with a failed in use swap partition.
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PostPosted: Thu Oct 04, 2012 7:06 pm    Post subject: Reply with quote

so use raid10 on all drives then ?
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PostPosted: Thu Oct 04, 2012 7:19 pm    Post subject: Reply with quote

Dark Foo,

except /boot
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PostPosted: Thu Oct 04, 2012 7:28 pm    Post subject: Reply with quote

raid1 for boot?
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PostPosted: Thu Oct 04, 2012 7:31 pm    Post subject: Reply with quote

Dark Foo,

Yes and pay attention to your metadata version.
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PostPosted: Thu Oct 04, 2012 7:33 pm    Post subject: Reply with quote

0.90 for boot - the others should be safe on the newer version i take it?

should i put the put the partitions as raid auto detect or leave them as linux native?

once i know this is should be good to go :)
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PostPosted: Thu Oct 04, 2012 8:05 pm    Post subject: Reply with quote

Dark Foo,

If you want raid auto assembly you must use ver 0.90 metadata and flag the partitions as type 0xfd

If you use later metadata, raid autoassembly will not work and for root on raid, you will need an inirrd/initramfs to assemble root before it can be mounted.
In this case, the partition type is not important.
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PostPosted: Thu Oct 04, 2012 9:09 pm    Post subject: Reply with quote

guess i have enough information to get things going, guess i wont need a big swap on that machine as it will be on near all the time without it going to sleep, good to know i was right about swap for laptop :)

thanks neddy
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PostPosted: Sun Oct 07, 2012 9:13 am    Post subject: Reply with quote

Well here goes nothing!!!!! :lol:

is 512K chunk size too much, seems that the default it wants to go for
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PostPosted: Sun Oct 07, 2012 11:10 am    Post subject: Reply with quote

Dark Foo,

If you don't know and reading the man page does not help, go with the default.
The reality is that thee is no single chunk size that suits all hardware and file system content.
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PostPosted: Sun Oct 07, 2012 11:12 am    Post subject: Reply with quote

doesnt help googling it as every suggests a different size for the same sort of raid, have gone with 512 and will see how the system performs, if it's not as good as i think i can always try something else :)

Thanks for the help Neddy much appropriated
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