Re: [zfs-discuss] Drive Failure w/o Redundancy

2007-06-26 Thread Richard Elling

Jef Pearlman wrote:

Hi. I'm looking for the best solution to create an expandable heterogeneous 
pool of drives. I think in an ideal world, there'd be a raid version which 
could cleverly handle both multiple drive sizes and the addition of new drives 
into a group (so one could drop in a new drive of arbitrary size, maintain some 
redundancy, and gain most of that drive's capacity), but my impression is that 
we're far from there.


Mirroring (aka RAID-1, though technically more like RAID-1+0) in ZFS will do 
this.


Absent that, I was considering using zfs and just having a single pool. My main question 
is this: what is the failure mode of zfs if one of those drives either fails completely 
or has errors? Do I permanently lose access to the entire pool? Can I attempt to read 
other data? Can I "zfs replace" the bad drive and get some level of data 
recovery? Otherwise, by pooling drives am I simply increasing the probability of a 
catastrophic data loss? I apologize if this is addressed elsewhere -- I've read a bunch 
about zfs, but not come across this particular answer.


We generally recommend a single pool, as long as the use case permits.
But I think you are confused about what a zpool is.  I suggest you look
at the examples or docs.  A good overview is the slide show
http://www.opensolaris.org/os/community/zfs/docs/zfs_last.pdf


As a side-question, does anyone have a suggestion for an intelligent way to 
approach this goal? This is not mission-critical data, but I'd prefer not to 
make data loss _more_ probable. Perhaps some volume manager (like LVM on linux) 
has appropriate features?


ZFS, mirrored pool will be the most performant and easiest to manage
with better RAS than a raidz pool.
 -- richard
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[zfs-discuss] Drive Failure w/o Redundancy

2007-06-26 Thread Jef Pearlman
Hi. I'm looking for the best solution to create an expandable heterogeneous 
pool of drives. I think in an ideal world, there'd be a raid version which 
could cleverly handle both multiple drive sizes and the addition of new drives 
into a group (so one could drop in a new drive of arbitrary size, maintain some 
redundancy, and gain most of that drive's capacity), but my impression is that 
we're far from there.

Absent that, I was considering using zfs and just having a single pool. My main 
question is this: what is the failure mode of zfs if one of those drives either 
fails completely or has errors? Do I permanently lose access to the entire 
pool? Can I attempt to read other data? Can I "zfs replace" the bad drive and 
get some level of data recovery? Otherwise, by pooling drives am I simply 
increasing the probability of a catastrophic data loss? I apologize if this is 
addressed elsewhere -- I've read a bunch about zfs, but not come across this 
particular answer.

As a side-question, does anyone have a suggestion for an intelligent way to 
approach this goal? This is not mission-critical data, but I'd prefer not to 
make data loss _more_ probable. Perhaps some volume manager (like LVM on linux) 
has appropriate features?

Thanks for any help.

-puk
 
 
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