Re: [POC] disaster recovery: reconstruct all shards

[Gandalf Corvotempesta <gandalf.corvotempesta@xxxxxxxxx>]

That's why I'm asking for a native tool from gluster

Il 1 mar 2017 2:46 PM, "Krutika Dhananjay" <kdhananj@xxxxxxxxxx> ha scritto:

The caveats are:

1. A non-existent/missing shard anywhere between offset $SHARD_BLOCK_SIZE through ceiling ($FILE_SIZE/$SHARD_BLOCK_SIZE)

indicates a hole. When you reconstruct data from a sharded file of this nature, you need to take care to retain this property.

2. The above is also true for partially filled shards between offset $SHARD_BLOCK_SIZE through ceiling ($FILE_SIZE/$SHARD_BLOCK_SIZE).

What do I mean by partially filled shards? Shards whose sizes are not equal to $SHARD_BLOCK_SIZE.

In the above, $FILE_SIZE can be gotten from the 'trusted.glusterfs.shard.file-size' extended attribute on the base file (the 0th block).

-Krutika

On Mon, Feb 27, 2017 at 1:45 PM, Gandalf Corvotempesta <gandalf.corvotempesta@gmail.com> wrote:

Which caveats?

Anyway, having this recovery tool integrated in gluster could be an appreciable plus to guarantee data recovery natively

Il 27 feb 2017 6:02 AM, "Krutika Dhananjay" <kdhananj@xxxxxxxxxx> ha scritto:

It should be possible to write a script that stitches the different pieces of a single file together

(although with a few caveats).

-Krutika

On Sun, Feb 26, 2017 at 8:52 PM, Gandalf Corvotempesta <gandalf.corvotempesta@gmail.com> wrote:

Would be possible to add a command to use in case of disaster recovery
(where everything is broken) to recreate files from sharding ?

In example, let's assume a totally down cluster. no trusted pools and
so on but sysadmin knows which hdd is part of any distributed replica:

hdd1 + hdd2 + hdd3 are distributed and replicated to hdd4 + hdd5 + hdd6

a CLI could traverse hdd1,hdd2,hdd3 and reconstruct all shards
creating the original, unsharded file.
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