Swapping on SSD, and heavy swapping
Hello fellow future Linux admins ;-)
Is there something to take care of when setting up swap space on an SSD?
In particular concerning the reliability of the system?
Below are my thoughts; what I am interested in is:
- do you have own experiences in that regard? (the failures, the recoveries)
- links you know of to articles that discuss these issues
Thanks, and happy studying! Christian
I heard some reasons why swapping is good or required over the past years (without formal Linux education) :
- it allows the kernel to move unused pages (from unused/sleeping code or unused/irrelevant data) out of the hot RAM, and thus to utilize the RAM better (for buffering, for caching, for more space for actually active code/data)
- I think this was important when free RAM was scarce; these days, I have some systems running stable without any swap partition
- it was/is used as backing space for hibernation
- I think this is only relevant for laptops and desktop machines, not for server machines (or server VMs)
In the ages of HDD and insufficient RAM there often were times when heavy swapping set in. With regard to SSD, I see two differences that make me skeptical:
- the wear was on the mechanics lifetime (HDD), not on the flash lifetime (SSD)
- HDD mechanics could be (probably were) designed to life with high-cycle-fatigue, whereas SSD flash has a nominal limit for write/erase-cycles
- so I expect SSD swapping will eventually fail, depending to some degree on the load pattern and on the quality of the SSD
- the sluggish nature of mechanics meant that HDD-swapping throttles the system independently of age (of remaining lifetime)
- that works like a counter measure; when the system is overloaded, instead of just burning through, it will also throttle down
- you get a performance feedback always and instantly, regardless of the remaining lifetime of the HDD/SSD component, so you are triggered to react long before the HDD/SSD is actually about to fail
Regarding that, what I wonder is:
- if frequent swapping is expected, would it still be best practice to put the Linux, the user software/data, and the swap on one SSD device? Or is the best practice to invest in a separate device for swap, even if this will raise the price?
- are there soft measures?
- (maybe to partition SSD flash, so the wear of one partition will not harm the life expectation of another partition - I don't think that is technically implemented, I think each SSD is just one black box, unlike the magnetic tracks of the HDD you cannot tell which flash cells will be used)
- what is the hard impact?
- I'd expect that, when all three - OS, user software/data, and swap - are one one partition, sudden death due to heavy swapping will then also destroy the OS and user software/data
- or are there ways to soften the failure of the swap device
Comments
-
It is not that complicated. If you are swapping all the time, either get more RAM or don't use the machine this way, or make sure the swap device is not SSD. Or you can use zswap which uses compressed memory for swap -- fedora now does this by default, but it can be minor league tricky to set up.
Any system which depends on using swap often is broken to begin with. A lot of folks, including me, tend to just not use swap anymore.
1
Categories
- All Categories
- 60 LFX Mentorship
- 113 LFX Mentorship: Linux Kernel
- 618 Linux Foundation IT Professional Programs
- 321 Cloud Engineer IT Professional Program
- 142 Advanced Cloud Engineer IT Professional Program
- 55 DevOps Engineer IT Professional Program
- 68 Cloud Native Developer IT Professional Program
- 6 Express Training Courses
- 6 Express Courses - Discussion Forum
- 2.3K Training Courses
- 19 LFC110 Class Forum - Discontinued
- 9 LFC131 Class Forum
- 31 LFD102 Class Forum
- 176 LFD103 Class Forum
- 22 LFD121 Class Forum
- 2 LFD137 Class Forum
- 61 LFD201 Class Forum
- 2 LFD210 Class Forum
- 1 LFD210-CN Class Forum
- 1 LFD213 Class Forum - Discontinued
- 128 LFD232 Class Forum - Discontinued
- LFD237 Class Forum
- 23 LFD254 Class Forum
- 654 LFD259 Class Forum
- 108 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- 4 LFD273 Class Forum
- 2 LFS145 Class Forum
- 28 LFS200 Class Forum
- 740 LFS201 Class Forum - Discontinued
- 1 LFS201-JP クラス フォーラム
- 12 LFS203 Class Forum
- 92 LFS207 Class Forum
- 301 LFS211 Class Forum
- 54 LFS216 Class Forum
- 47 LFS241 Class Forum
- 41 LFS242 Class Forum
- 37 LFS243 Class Forum
- 12 LFS244 Class Forum
- 41 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- LFS251 Class Forum
- 143 LFS253 Class Forum
- LFS254 Class Forum
- LFS255 Class Forum
- LFS256 Class Forum
- LFS257 Class Forum
- 1.2K LFS258 Class Forum
- 10 LFS258-JP クラス フォーラム
- 106 LFS260 Class Forum
- 145 LFS261 Class Forum
- 39 LFS262 Class Forum
- 83 LFS263 Class Forum - Discontinued
- 15 LFS264 Class Forum - Discontinued
- 11 LFS266 Class Forum - Discontinued
- 20 LFS267 Class Forum
- 18 LFS268 Class Forum
- 26 LFS269 Class Forum
- 204 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- LFS274 Class Forum
- 3 LFS281 Class Forum
- 249 LFW211 Class Forum
- 177 LFW212 Class Forum
- 9 SKF100 Class Forum
- SKF200 Class Forum
- 907 Hardware
- 220 Drivers
- 74 I/O Devices
- 44 Monitors
- 116 Multimedia
- 210 Networking
- 102 Printers & Scanners
- 86 Storage
- 764 Linux Distributions
- 88 Debian
- 66 Fedora
- 15 Linux Mint
- 13 Mageia
- 24 openSUSE
- 143 Red Hat Enterprise
- 33 Slackware
- 13 SUSE Enterprise
- 357 Ubuntu
- 482 Linux System Administration
- 40 Cloud Computing
- 70 Command Line/Scripting
- Github systems admin projects
- 95 Linux Security
- 80 Network Management
- 108 System Management
- 51 Web Management
- 72 Mobile Computing
- 25 Android
- 32 Development
- 1.2K New to Linux
- 1.1K Getting Started with Linux
- 545 Off Topic
- 132 Introductions
- 223 Small Talk
- 22 Study Material
- 831 Programming and Development
- 282 Kernel Development
- 515 Software Development
- 974 Software
- 260 Applications
- 185 Command Line
- 3 Compiling/Installing
- 119 Games
- 318 Installation
- 65 All In Program
- 65 All In Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)