• Diff for "SSDOptimization"

Translation(s): none

This page is about optimal set up of a SSD (Solid State Drive). This page should be keep it clean enough for beginners to get the most basic idea.

Basics

• Avoid TLC (Triple Layer Cell)-based SSDs; they have fewer write cycles than MLC (Multi Layer Cell)-based SSDs.
• Use a recent Linux kernel (3.2 or newer). Note that SSD caching is only supported on Linux 3.9 or newer, so if you need it you will need to install it.
• Have enough RAM to not need any swap space under normal workloads while maintaining most of the variable data in a persistent RAMDISK that gets synced to disk periodically.
• To be able to suspend to disk (hibernate) and survive power outages or changing batteries, do set up a swap partition that is larger than your RAM, preferably on hdd. (There may be gigabytes of RAM content that gets written to disk.)
• Use the "noatime" (or "relatime") mount option in /etc/fstab, to disable (or reduce) disk writes during each disk read access. This also slightly improves performance, even on HDDs.
• Use the "discard" mount option in /etc/fstab, to enable TRIM support. Almost any SSD made since 2010 support TRIM. This prevents performance loss over time.
• Use the ext4 filesytem.
• Optionally, use the btrfs format (not yet stable). It supports additional mount options like "ssd" in /etc/fstab, that enables SSD optimized disk space allocation.

These may also help:

• https://wiki.archlinux.org/index.php/SSD

• http://siduction.org/index.php?module=news&func=display&sid=78

• http://forums.debian.net/viewtopic.php?f=16&t=76921

• http://wiki.ubuntuusers.de/SSD (German)

Partitions and Alignment

You should consider to use the Multi HDD/SSD Partition Scheme to keep variable and bulk data on the HDD(s) and establish a fallback redundancy, if the system also has a HDD available (internal or external spinning disk).

Since wheezy all tools should automatically align filesystems and partitions to the 4096 byte page size. This is one of the most important optimization aspects. Here are good links for this subject:

• Advanced Format

• Aligning SSD Partitions (Linux magazine)

• Aligning filesystems to an SSD’s erase block size] by Ted T'so (kernel FS developer)

• http://blog.nuclex-games.com/2009/12/aligning-an-ssd-on-linux/

• http://lifehacker.com/5837769/make-sure-your-partitions-are-correctly-aligned-for-optimal-solid-state-drive-performance

Mounting SSD filesystems

The performance of SSDs is also be influenced by filesystem mounting options:

• Add the"noatime" mount option in /etc/fstab to avoid writing the access time whenever a file is read.

• Maybe enable the "discard" filesystem options for automatic/online TRIM. However, this is not strictly necessary if your SSD has enough overprovisioning (spare space) or you leave (unpartitioned) free space on the SSD (http://www.spinics.net/lists/raid/msg40866.html). Enabling online-trim in fstab may just slow down some SSDs significantly (https://patrick-nagel.net/blog/archives/337).

  • Set "discard" mount option in /etc/fstab for the ext4 filesystem, swap partition, Btrfs, etc. See mount(8).
  • Set "issue_discards" option in /etc/lvm/lvm.conf for LVM. See lvm.conf(5).
  • Set "discard" option in /etc/crypttab for dm-crypt.

Note that using discard with on-disk-cryptography (like dm-crypt) also has drawbacks with respect to security/cryptography! See crypttab(5).

dm-crypt's /etc/crypttab:

#<target name>    <source device>            <key file>  <options>
var  UUID=01234567-89ab-cdef-0123-456789abcdef  none  luks,discard

• You'll also need to update your initramfs: update-initramfs -u -k all

• Optionally, set up an offline-trim cronjob that runs time fstrim -v  (or mdtrim) on the ssd mountpoints periodically. Until software raid (md device layer) has trim support, you could use something like mdtrim (https://github.com/Cyberax/mdtrim/).

Reduction of SSD write frequency via RAMDISK

Use of RAMDISK can stop constantly changing files from hitting on the SSD (it may hit SSD via swap). RAMDISK configuration may be performed via

• Set RAMTMP, RAMRUN and RAMLOCK to "yes" (in /etc/default/rcS or /etc/default/tmpfs since wheezy)
• /etc/fstab: line such as "tmpfs /tmp noatime,nosuid 0 0"
• Optionally, make system only flush data to the disk every 10 minutes or more:
  • Kernel settings like the "dirty_buffer_ratio" etc. may only be available as non-path/mount specific global settings.
  • Mount option "commit=600" in /etc/fstab. See mount(8).

  • Or better, use pm-utils (Debian BTS #659260), tlp, or laptop-mode-tools (also optimizes read buffers) to configure the laptop-mode even under AC operation.

  Attention: Increasing the flushing interval from the default 5 seconds (maybe even until proper shutdown) leaves your data much more vulnerable in case of lock-ups or power failures, and seems to be a global setting.

Enabling RAMTMP may cause some (broken) applications to run out of temporary write disk space. Setting TMPDIR environment variable for those programs pointing to a writable disk space should fix their situation.

Please note files in /tmp are wiped out upon reboot unless /etc/default/rcS is set to something other than TMPTIME=0 (if not set, 0 is the default value).

Persistent RAMDISK

As an advanced option, you may consider to use persistent RAMDISK (dedicated read/write RAM buffer that gets synced periodically and on startup/shutdown) with anything-sync-daemon or goanysync set up:

• /home (synced to work-data-fs raid only once a day?), you only risk settings the true work in /home/*/work-data is on a dedicated raid
• /home/*/work-data/volatile (synced more frequently, once per hour?)
• /home/*/Downloads (synced to bulk-data-fs once a day?)
• /var completely if supported (syncing once a day? avoids spin-ups and allows to save /var also to SSD), at least set this up for
  • /var/log if supported
  • /var/cache/apt/archives
    • Configure apt to delete package files after installing, to minimize the data to sync.

Options to having logs copied into RAM:

• http://www.debian-administration.org/articles/661

• http://www.tremende.com/ramlog

• https://github.com/graysky2/anything-sync-daemon (if it supports this)

• https://github.com/wor/goanysync

If /home is not on a persistent ramdisk, use profile-sync-daemon to have the browser database and cache copied into RAM during uptime (http://ubuntuforums.org/showthread.php?t=1921800 https://github.com/graysky2/profile-sync-daemon)

• /home/*/<browser-cache-and-profiles> (synced to root-fs or home-fs)

Further improvement: Patch anything-sync-daemon or goanysync to use a (copy-on-write) union filesystem mount (e.g. http://aufs.sourceforge.net) to keep changes in RAM and only save to SSD on unmount/shutdown (aubrsync), instead of copying all data to RAM and having to sync it all back.

Low-Latency IO-Scheduler

The default I/O scheduler queues data to minimize seeks on HDDs, which is not necessary for SSDs. Thus, use the deadline scheduler that just ensures bulk transactions won't slow down small transactions: Install sysfsutils and

• echo "block/sdX/queue/scheduler = deadline" >> /etc/sysfs.conf

(adjust sdX to match your SSD) reboot or

• echo deadline > /sys/block/sdX/queue/scheduler

The dumb "noop" scheduler may be a little faster in benchmarks that max out the throughput, but cause noticeable delays for other tasks when large file transfers are going on.

/etc/fstab example

Here is an example of /etc/fstab

# /etc/fstab: static file system information.
#
# Use 'vol_id --uuid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
### SSD: discard,noatime
### match battery operation default for commit JOURNAL_COMMIT_TIME_AC in Add files in /etc/pm/config.d/*
/dev/mapper/goofy-root /               ext4    discard,noatime,commit=600,errors=remount-ro 0       1
# /boot was on /dev/sda1 during installation
UUID=709cbe4a-80c1-46cb-8bb1-dbce3059d1f7 /boot           ext4    discard,noatime,commit=600,defaults        0       2
### SSD: discard
/dev/mapper/goofy-swap none            swap    sw,discard              0       0
/dev/mapper/goofy-chroot /srv/chroot         btrfs    ssd,discard,noatime 0       2
/dev/scd0       /media/cdrom0   udf,iso9660 user,noauto     0       0

/etc/lvm/lvm.conf example

...
# This section allows you to configure which block devices should
# be used by the LVM system.
devices {
...
    # Issue discards to a logical volumes's underlying physical volume(s) when
    # the logical volume is no longer using the physical volumes' space (e.g.
    # lvremove, lvreduce, etc).  Discards inform the storage that a region is
    # no longer in use.  Storage that supports discards advertise the protocol
    # specific way discards should be issued by the kernel (TRIM, UNMAP, or
    # WRITE SAME with UNMAP bit set).  Not all storage will support or benefit
    # from discards but SSDs and thinly provisioned LUNs generally do.  If set
    # to 1, discards will only be issued if both the storage and kernel provide
    # support.
    # 1 enables; 0 disables.
    #issue_discards = 0
    issue_discards = 1
}
...

Smaller system with SSD

See

• http://wiki.debian.org/DebianAcerOne?highlight=%28SSD%29#Reducing_Disk_Access_for_laptops_with_SSDs