Request for opinions - gvinum or ccd?

[krad]

You shouldn't need to alter the copies attribute to recover from disk
failures as the normal raid should take care of that. What the copies is
useful for is when you get undetected write errors on the drive due to crc
collisions or the drive simply being rubbish

Zfs will intelligently assign the copies across multiple drives if possible,
so if you had 3 vdevs and copies set to three, One copy should end up on
each vdev. Note this isn't the same as mirroring, as each vdev could be a
raidz2 group. With copies=1 you would get a 3rd of the file on each. With
copies 3 you would get a full version of each.

This is obviously very costly on drive space though. It is tunable per file
system though so you don't have to enable it for the whole pool just the
bits you want.

-----Original Message-----
From: owner-freebsd-hackers at freebsd.org
[mailto:owner-freebsd-hackers at freebsd.org] On Behalf Of Wojciech Puchar
Sent: 01 June 2009 01:26
To: Mike Meyer
Cc: freebsd-hackers at freebsd.org; xorquewasp at googlemail.com
Subject: Re: Request for opinions - gvinum or ccd?

>    Disks, unlike software, sometimes fail. Using redundancy can help

modern SATA drives fail VERY often. about 30% of drives i bought recently 
failed in less than a year.

> both checksum on and copies > 1 on, and the latter isn't the
> default. It's probably better to let zpool provide the redundancy via
> a mirror or raid configuration than to let zfs do it anyway.

ZFS copies are far from what i consider useful.

for example you set copies=2. You write a file, and get 2 copies.

Then one disk with one copy fails, then you put another, do resilver but 
ZFS DOES NOT rebuild second copy.

You need to write a program that will just rewrite all files to make this.
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