Configuring SSD Drives for Write Journaling

Using SSD drives for write journaling can help you reduce write latencies, thus improving the overall cluster performance.

To determine how much SSD space you will need for the journals, use the pstorage advise-configuration command. For example:

# pstorage -c pstorage1 advise-configuration --cs /hdd1 --cs /hdd2 --cs /hdd3 --ssd /ssd -m /mnt/pstorage

You have the following setup:

CS on /hdd3 -- Total disk space 125.9GB

CS on /hdd2 -- Total disk space 125.9GB

CS on /hdd1 -- Total disk space 97.2GB

SSD on /ssd -- Total disk space 12.4GB

Proposed server configuration

- 5.4GB (43%) for CS journals, 5.4GB (43%) for mount read cache,

1.5GB (12%) reserved (including 349MB checksums for 349.2GB of data)

- CS journal sizes:

1.9GB for /hdd3

1.9GB for /hdd2

1.5GB for /hdd1

How to setup the node:

pstorage -c pcs1 make-cs -r /hdd3 -j /ssd/cs3-pcs1-journal -s 2015

pstorage -c pcs1 make-cs -r /hdd2 -j /ssd/cs2-pcs1-journal -s 2015

pstorage -c pcs1 make-cs -r /hdd1 -j /ssd/cs1-pcs1-journal -s 1555

pstorage-mount -c pcs1 /mnt/pstorage -C /ssd/pstorage-pcs1-cache -R 5585

Mount option for automatic cluster mount from /etc/fstab:

pcs1 /mnt/pstorage fuse.pstorage cache=/ssd/pstorage-pcs1-cache,cachesize=5585

Note:

1. If you have multiple chunk servers on a single host, create a separate SSD journal for each CS, making sure that the SSD has enough space for all CS journals.To modify the size of existing CS journals use the pstorage configure-cs command.

2. When deciding on a journal size without using the pstorage advise-configuration command, make sure there is 1GB of SSD space per each 1TB of HDD space for checksums.