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https://issues.apache.org/jira/browse/HDFS-8888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14713425#comment-14713425
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Walter Su commented on HDFS-8888:
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I can't wait to take a look at detailed design. Right now, I just want to
compare "volume" in LVM, btrfs with HDFS.
The top motivation of logic volume in LVM is for space
partition(pre-allocation). It has namespace and space isolation. You must don't
want a normal volume shares the same namespace with a raid volume. File
migration between volumes usually requires data migration/conversion.
HDFS has no space isolation because blocks locate on all DNs. So there is no
need to keep namespace isolation anymore. We can rename files under the one
namespace without data migration.
Federation brings namespace scalability, and also namespace isolation. It's
more suitable for multi-tenant environment but not for one application or one
user.
"subvolume" in btrfs shares one device. So there is no space isolation. But it
keeps namespace isolation. I think one reason is for easier snapshot(and etc.)
implementation and a better view(with mount). I agree what Andrew said, we've
already implemented at the directory-level. I think it's just fine. I don't
quite agree namespace isolation can simplify the management. If you ground a
good student, can you make he/she get higher scores in exam? Although I believe
encryption zone should be isolated for security reason, and I think rename
restriction works fine.
> Support volumes in HDFS
> -----------------------
>
> Key: HDFS-8888
> URL: https://issues.apache.org/jira/browse/HDFS-8888
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Haohui Mai
>
> There are multiple types of zones (e.g., snapshottable directories,
> encryption zones, directories with quotas) which are conceptually close to
> namespace volumes in traditional file systems.
> This jira proposes to introduce the concept of volume to simplify the
> implementation of snapshots and encryption zones.
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