Difference between revisions of "SSD"

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=Accumulated info on how to use your SSD drive under linux=
#REDIRECT [[Solid State Drives]]
''under construction, not complete, not nice''
So you got yourself one of those precious, blazing fast SSDs and you want to get the most out of it? There are a number of things to worry about, such as alignment, choice of file system, journaling and TRIM.
==Before buying==
Make sure the SSD you buy has a firmware with TRIM support. This is a vital feature that both prolongs your SSDs lifetime and reduces the loss of performance over time to almost nil. I recommend all of what Anand has ever written about SSDs in general before considering to buy one:
SSD Anthology (history lesson, a bit dated): http://www.anandtech.com/show/2738
SSD Relapse (refresher and more up to date: http://www.anandtech.com/show/2829
He also reviewes most of the SSDs so you'll find up-to-date benchmarks on all of them. Brilliant stuff.
==Setting up a fresh drive with archlinux==
This guide assumes that you want to install archlinux from scratch on your brand new SSD. For different applications (like using them in a RAID, a server or whatever) many things might be different
===Step 1: Aligning the drives partitions===
Launch the latest archlinux install medium, then go on launching fdisk with fixed head and sector number options. The head and sector options are a safe bet for many drives. Read the links below to find out more about what they do, as some SSDs might require a different setting for maximum performance.
# fdisk -H 32 -S 32 /dev/sda
Now create your partitions.
{{Warning|When creating the first partition, select cylinder number 2 as the first cylinder, not 1. This ensures that your first partition doesn't get shifted.}}
You might not want to create a swap partition if you don't really need it.
==== Background info ====
aligning the SSD to block boundaries:
aligning the SSD to block boundaries when using LVM:
===Step 2: Choosing a file system===
There's lots of talk about what to use. Some say ext2 should be used because it doesn't have journaling, some say ext4 without journaling is best, and some use btrfs. Since TRIM support, journaling can be enabled without much of a drawback as stated by the guy in the link below. If you disable journaling, you end up with a slightly faster system, but in case of a power failure your data might end up garbled. I decided to go with a regular journaled ext4 because it's a laptop and a low battery could garble me some data. If you plan on using a RAID, there's even more to consider, such as stripe-widths and so on.
# mkfs.ext4 /dev/sda1
Next, consider which mount flags to use in the entries for your partitions in [[fstab|/etc/fstab]] (see the reasons in the link below):
/dev/sda1 / ext4 defaults,noatime,discard 0 1
{{Note|Omitting the discard option will leave the partition ignoring the TRIM command!}}
====Background info====
*btrfs on an SSD on arch: [http://www.madeo.co.uk/?p=346 Intel X25-M Gen2 on linux – migrating to btrfs on kernel 2.6.33]
*Thoughts on why journaling isn't much of a deal: [http://thunk.org/tytso/blog/2009/03/01/ssds-journaling-and-noatimerelatime/ SSD’s, Journaling, and noatime/relatime ]
===Other SSD Tweaks to Consider===
==== RAID LVM Usage ====
Place holder for this section.
==== SWAP Space on and SSD ====
If you decided to use a swap partition or file, it's recommended to reduce the "swapiness" of the system to avoid writes to swap. Add this to rc.local:
# echo 1 > /proc/sys/vm/swapiness
==== I/O Scheduler Change for SSD ====
Consider switching from the cfq scheduler to the noop or deadline scheduler.  Using the noop scheduler for example simplifies requests in the order they are received, without giving any consideration to where the data physically resides on the disk.  This option is thought to be advantageous SSDs since seek times are identical for all sectors on the disk.
To see which scheduler your system is using, view the contents of /sys/block/sda/queue/scheduler:
cat /sys/block/sda/queue/scheduler
The scheduler currently in use is listed in brackets:
[noop] deadline cfq
To force your system to use the noop scheduler by default, add the following line to your /etc/rc.local file:
# echo noop > /sys/block/sda/queue/scheduler
=====Background info=====
More on disk schedulers: http://www.linux-mag.com/id/7564/1/

Latest revision as of 20:48, 1 July 2010

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