MySQL tables on external hard drive

Question

I have a large amount of text data I need to import into MySQL. I'm doing this on a MacBook and don't have enough space for it so I want to store it in an external hard drive (I'm not really concerned about speed at this point - this is just for testing).

What's the best way to do it?

• Install MySQL on the external hard drive (is this possible on a Mac?)
• Install MySQL on the laptop's hard drive and have the tables on the external (how?)

Darwindarwinian

Answer 1

One simple hack is to create an symbolic link replacing your current mysql database file location pointing to the external disk. Google symbolic link.

sample usage would be after you shutdown mysql, change the old mysql db folder name to something else, and create the symbolic link using the ln command like below

ln -s [EXTERNAL DRIVE PATH] [MYSQL DB FOLDER PATH]

Then move all the previous content of the mysql db folder to the new location.

Alcoholic

This is half the procedure. You will need to add the following lines to "/etc/apparmor.d/usr.sbin.mysqld"\n /external/drive/path/ r, /external/drive/path/** rwk,\n else you get:\n 121210 8:36:18 [Warning] Can't create test file /external/drive/path/hostname.lower-test 121210 8:36:18 [Warning] Can't create test file /external/drive/path/hostname.lower-test mysqld: Can't change dir to '/external/drive/path/' (Errcode: 13) 121210 8:36:18 [ERROR] Aborting – Cantabile

Answer 2

Open /etc/mysql/my.cnf and find the value of the datadir. Alternatively, you can find this out in the mysql monitor with

mysql>   select @@datadir;

Stop mysql

sudo systemctl stop mysql

Copy the data from there to your external drive

sudo rsync -av /var/lib/mysql /mnt/myHDD/somedir/mysql

Modify the location of the datadir in my.cnf.
Start mysql again

sudo systemctl start mysql

Verify that everything is still fine and remove the original data dir.

This page contains a more extensive guide but all the additional issues it warns about were not relevant for me on my raspberry PI. I.e. I skipped them and it worked.

Reflect

Answer 3

For the second option, a tablespace might do the trick:

http://dev.mysql.com/doc/refman/5.1/en/create-tablespace.html

Prince

Answer 4

User user658991 answer is halfway there.

After adding the soft link, you will need to add the following line to /etc/apparmor.d/usr.sbin.mysqld beneath the 2 lines to the old mysql folder.

/path/to/mysql/folder/on/the/external/ r
/path/to/mysql/folder/on/the/external/ ** rwk

Without these 2 lines, MySQL fails to start complaining of:

Can't create test file /path/to/mysql/folder/on/the/external/hostname.lower-test
Can't create test file /path/to/mysql/folder/on/the/external/hostname.lower-test
mysqld: Can't change dir to '/path/to/mysql/folder/on/the/external/' (Errcode: 13)

Restart apparmor for the changes to take effect.

sudo invoke-rc.d apparmor restart

With this, MySQL starts normally.

Cantabile

Can this be done while maintaining all my databases on the HD and adding a new one on and external HD? – Painty

@aresnelupin yes, all your databases will be maintained. – Cantabile

This was not required for me with MySQL Version 5.5.60-0+deb8u1. – Interactive