I accidentally deleted my partition table(MBR + NTFS) on my old disk through:
gpart delete -i ada3
gpart destory ada3
Which contains all files on it. How can I restore these data on this disk?
After partitioning a new drive with an MBR, you should run gpart backup, save the output and store it somewhere safe. Then you can restore it with gpart restore.
If you use a GPT, the backup is made automatically. You can then use gpart recover to recover it.
Related
I am using greenplum DB's gpbackup utility to take incremental backup of database, through following commands
1: Full backup
gpbackup --dbname incdb --backup-dir /data/gpbackups --leaf-partition-data
2: Then I added some rows and took incremental backup as:
gpbackup --dbname incdb --backup-dir /data/gpbackups --leaf-partition-data --incremental
But when I go to the backup folder, unzip the backed up files and read them in terminal, I see incremental backup files have all the data from start, instead of only changed data. Shouldn't it have only the data added after the full backup?
Please also guide me if remote backups are possible through gpbackup utility?
You can find more details here, regarding the implementation of Greenplum's Incremental Backup
https://gpdb.docs.pivotal.io/backup-restore/1-16/admin_guide/managing/backup-gpbackup-incremental.html
In short, incremental backups work best on AO partitioned tables.
gpbackup will identify which partitions of AO tables have data changes since the last full or incremental backup, and add those to the backup set.
Heap tables are always fully backed up, regardless of the incremental flag is used.
In your use case, were you using AO partitioned tables?
As the data in case of Cassandra is physically removed during compaction, is it possible to access the recently deleted data in any way? I'm looking for something similar to Oracle Flashback feature (AS OF TIMESTAMP).
Also, I can see the pieces of deleted data in the relevant commit log file, however it's obviously unreadable. Is it possible to convert this file to a more readable format?
You will want to execute a restore from your commitlog.
The safest is to copy the commitlog to a new cluster (with same schema), and restore following the instructions (comments) from commitlog_archiving.properties file. In your case, you will want to set restore_point_in_time to a time between your insert and your delete.
Is there a way to backup Cassandra directly to tape (streaming device)?
Or to perform real snapshots?
The snapshot Cassandra is referring to is not what I want to call a snapshot.
It is more a consistent copy of the database files to a directory.
Regards Tomas
First, let's clarify the Cassandra write path, so we know what we need to back up. Writes come in and are first journaled in the commitlog, then written to the memtable, then eventually flushed to sstables. When sstables flush, the relevant commitlog segments are deleted.
If you want a consistent backup of Cassandra, you need at the very least the sstables, but ideally the sstables + commitlog, so you can replay any data between the commitlog and the most recent flush.
If you're using tape backup, you can treat the files on disk (both commitlog and sstables) as typical data files - you can tar them, rsync them, copy them as needed, or point amanda or whatever tape system you're using at the data file directory + commitlog directory, and it should just work - there's not a lot of magic there, just grab them and back them up. One of the more common backup processes involves using tablesnap, which watches for new sstables and uploads them to s3.
You can backup Cassandra directly to Tape using SPFS
SPFS is a file system for Spectrum Protect.
Just mount the SPFS file system where you want the backups to land.
Eg
mount -t spfs /backup
And backup Cassandra to this path.
All operations that goes via this mountpoint (/backup), will automatically be translated to Spectrum Protect Client API calls.
On the Spectrum Protect backup server, one can use any type of supported media.
For instance: CD, Tape, VTL, SAS, SATA, SSD, Cloud etc..
In this way, you can easily backup your Cassandra directly to a backup server.
I have enabled the incremental backup in the cassandra.yaml file. As I know when we enable incremental backups, cassandra will backup the data (in backups directory) only when the memtable is flushed. But what if the memtable is yet to be flushed? I won't be able to get the incremental backup right?. I know that for the memtable to be flushed there are certain conditions to be met such as time interval or memtable space. My question is how do I modify this so that even if I enter one record after the last snapshot, I can still backup entire data along with that latest entry?
Consider this example
Take the snapshot.
Clear incremental backup (backups directory)
Enter a record to a table.
Check for the incremental backup in backups directory. It is still empty.
Now how do I backup the record which is written after the last snapshot?In general how do we backup the entire upto-date data unless we take the snapshot?
You can flush the files manually with nodetool flush just before taking the backup. That way you'll always have the latest memtable flushed.
nodetool docs
If you want to backup a cluster without taking a snapshot you can do it by simply saving everything under /data folder from every node (this includes mainly the .db files stats files etc).
In order to not override files you should store it with the token information as well.
When you want to restore from this backup, you should spin up a cluster with the same number of nodes, and simply copy the data, one-to-one from each backed-up node to a restored node. Pay attention that you'll have to modify cassandra.yaml to include the relevant token in cassandra.yaml (as well as the peers/seeds/etc) for each restored node.
After all the data is copied, you can start C* process on all the nodes.
I am looking for confirmation that my Cassandra backup and restore procedures are sound and I am not missing anything. Can you please confirm, or tell me if something is incorrect/missing?
Backups:
I run daily full backups of the keyspaces I care about, via "nodetool snapshot keyspace_name -t current_timestamp". After the snapshot has been taken, I copy the data to a mounted disk, dedicated to backups, then do a "nodetool clearsnapshot $keyspace_name -t $current_timestamp"
I also run hourly incremental backups - executing a "nodetool flush keyspace_name" and then moving files from the backup directory of each keyspace, into the backup mountpoint
Restore:
So far, the only valid way I have found to do a restore (and tested/confirmed) is to do this, on ALL Cassandra nodes in the cluster:
Stop Cassandra
Clear the commitlog *.log files
Clear the *.db files from the table I want to restore
Copy the snapshot/full backup files into that directory
Copy any incremental files I need to (I have not tested with multiple incrementals, but I am assuming I will have to overlay the files, in sequence from oldest to newest)
Start Cassandra
On one of the nodes, run a "nodetool repair keyspace_name"
So my questions are:
Does the above backup and restore strategy seem valid? Are any steps inaccurate or anything missing?
Is there a way to do this without stopping Cassandra on EVERY node? For example, is there a way to restore the data on ONE node, then somehow make it "authoritative"? I tried this, and, as expected, since the restored data is older, the data on the other nodes (which is newer) overwrites in when they sync up during repair.
Thank you!
There's two ways to restore Cassandra backups without restarting C*:
Copy the files into place, then run "nodetool refresh". This has the caveat that the rows will still be older than tombstones. So if you're trying to restore deleted data, it won't do what you want. It also only applies to the local server (you'll want to repair after)
Use "sstableloader". This will load data to all nodes. You'll need to make sure you have the sstables from a complete replica, which may mean loading the sstables from multiple nodes. Added bonus, this works even if the cluster size has changed. I'm not sure if ordering matters here (that is, I don't know if row timestamps are preserved through the load or if they're redefined during load)