[Gllug] Partioning advice needed

[Mike Brodbelt]

Anthony Newman wrote:
> 
> It's odd that init{rd,ramfs} used to be one of those optional things, 
> now people seem to see it as indispensable whether you actually need it 
> or not. I just consider it an extra hassle and a hack to make things 
> work that unfortunately became the norm.

I have always hated initrd, but initramfs is a different story. It
provides the best of both worlds - you get all your hardware support in
a single vmlinux file, and you can also get a "recovery console" if
things go wrong. Sticking a copy of your kernel+initramfs on a CD with
isolinux makes recovery pretty easy too, though with Knoppix, even
that't not always needed.

> You get what you pay for as usual; the sort of stuff I was alluding to 
> would probably cost a significant part of a person's lifetime salary 
> over its 3-5 year lifetime. There's no reason why the technology under 
> such things won't trickle down into the free implementations though, 
> provided it isn't too heavily patented.

It mostly has, IMO. Of course a percentage of the cost of the high end
stuff is raw hardware cost, but there's an obscene amount of markup on
the stuff.

> I'm being deliberately obtuse because I've been recently trying to make 
> Linux RAID/LVM go fast, stay fast and be able to be made to go faster 
> rather than just being able to store huge quantities of data (which is 
> in itself trivial), and it isn't particularly easy. Adding more disks to 
> try and give you greater throughput doesn't work if your data stays in 
> the same place on the platters afterwards.

Try ZFS (http://opensolaris.org/os/community/zfs/): -

# zpool iostat 1
               capacity     operations    bandwidth
pool         used  avail   read  write   read  write
----------  -----  -----  -----  -----  -----  -----
splash      11.2G  20.0T     96    289  11.3M  34.6M
splash      11.2G  20.0T      0  4.15K      0   531M
splash      11.2G  20.0T      0  3.98K      0   509M
splash      11.2G  20.0T      0  3.99K      0   511M
splash      18.2G  20.0T      0  1.56K      0   101M
splash      18.2G  20.0T      0      0      0      0
splash      18.2G  20.0T      0      0      0      0
splash      18.2G  20.0T      0      0      0      0
splash      18.2G  20.0T      0    727      0  90.9M
splash      18.2G  20.0T      0  3.42K      0   438M
splash      18.2G  20.0T      0  4.21K      0   539M
splash      18.2G  20.0T      0  4.19K      0   536M
splash      18.2G  20.0T      0  4.00K      0   511M
splash      18.2G  20.0T      0  3.71K      0   475M
splash      18.2G  20.0T      0  3.83K      0   490M

Those figures from Ben Rockwood's blog at cuddletech. Half a gig a
second fast enough? OK, so that's not a cheap piece of hardware, but
it's a hell of a lot cheaper per Terabyte than anything else you're
likely to get.

> I've also seen no mention of parity scrubbing of RAID 4/5/6 arrays under 
> Linux; anyone know if it's possible? I saw 500GB of data go down the pan 
> last year because of an undetected disk error on a 14 disk RAID5 array. 
> Which was nice.

I kind of hate to plug Solaris on a Linux list, especially as I mostly
prefer Linux, but there are some areas where it just beats everything
else out there. ZFS is one - end to end 64 bit checksumming of all data.
It's *better* than a parity scrub. But if you want to scrub "zpool scrub
 filesys" will do it nicely.

> I probably should have mentioned that I was thinking "while both online 
> and mounted" in the same thought, although I failed to mention that at 
> any point.

<broken_record>
"zpool add filesys mirror c5t1d0 c6t1d0"
</broken_record>

All online, of course.

I'm not normally a technical fanboy, and the Solaris userland has a long
way to go before it could be regarded as pleasant, but there are some
things that Sun have just done *really* well, and ZFS is IMO the best by
far. Much as I love XFS on LVM on RAID, there's nothing out there that
can touch ZFS right now. Nexenta even gives you a very Debian like
environment to play with it in, so you don't have to live with all the
weirdness you get with Solaris.

The only drawbacks right now are that you can't boot from it, and
there's no backup utility as good as xfsdump/xfsrestore, which is one of
the things I really like about XFS.

Mike
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