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59 Dell EMC SC Series Arrays with MySQL | 3063-BP-O
7. Restart MySQL.
service mysqld start
4.6 Ext4 file systems and MySQL
Because ext4 supports the SCSI UNMAP command, Dell EMC recommends using ext4 file systems for at
least the datadir location. SCSI UNMAP allows space to be reclaimed in SC Series arrays (version 5.4 or
newer). If a MySQL MyISAM or InnoDB file-per-table tablespace is truncated or deleted, the filesystem will
release the space and SC Series arrays will return the space back to it pagepool. MySQL supports other file
systems too, but if space reclamation is important, then it is recommended to use ext4. To enable space
reclamation functionality, the discard flag must be issued when mounting the ext4 filesystem or placed in file
/etc/fstab.
# mkfs -t ext4 /dev/mapper/mysql-inst1
# mount –o discard /dev/mapper/mysql-inst1 /mysql1
From /etc/fstab, it might look like this:
/dev/mapper/mysql-inst1 /mysql1 ext4 defaults,discard 0 0
Dell EMC strongly recommends that ext4 file systems be created on the entire disk, and not on a logical or
primary partition. This is due to the amount of careful planning and consideration, and to the level of
advanced knowledge of Linux systems that would be required to expand the underlying volume. Expanding a
file system that resides directly on a physical disk is much less complicated and risky.
For more information see the article, Native Free Space Recovery in Red Hat Linux, and additional material
from the subscription-based Red Hat Customer Portal.
4.7 Expanding SC Series volumes
Expanding file systems that reside on a logical or primary partition is not recommended. However, expanding
file systems that reside on the entire physical disk is. As with any partition or filesystem operation, there is
some risk of data loss. Dell EMC recommends creating a snapshot of the entire database using a consistent
snapshot profile prior to expanding a volume. Creating the snapshot will require the use of FLUSH TABLES
WITH READ LOCK in MySQL before the snapshot is created.
For more information on volume expansion, refer to:
• Dell EMC SC Series with Red Hat Enterprise Linux 6x best practices
• Section 4.4.1, InnoDB table type, tablespaces, and SC Series snapshots and space reclamation
• Section 5, MySQL backups and SC Series snapshots