Tag: swap

Enable zRAM as swap in Linux

Posted on by Bian Xi Leave a Comment on Enable zRAM as swap in Linux

Enable zRAM as swap in Linux

The problem with swap on SD boot OS, such as Raspberry Pi 4, is slow and increase SD write counts, in fact, SD card is slower than hard disk and expensive. For Raspberry Pi 4, it has 8 GB ram, enough for normal operation, but if don't turn on swap, there is no visibility of current memory usage whether causing memory swapping.

Traditional swap space

Fixed swap partition is rquired if use traditional swap space. Some facts as below

  • Fixed swap partition is rquired
  • Hard to resize or move
  • Waste storage space if it is not using most of time

Loopback device as swap

To have dynamic swap device, create a regular file and make it as loopback block device for swap, is a solution to have no fixed partition. The steps as below.

  • Create a file with fixed size using dd or some other commands
  • Create loopback device on newly created file
  • Init swap on loopback device using mkswap command
  • Change /etc/fstab to point to the new device

Issue as below

  • The loopback device needs to be initialized everytime after reboot

File as swap

In fact, swap can be directly created on file as below.

  • Create a file with fixed size using dd or some other commands
  • Init swap on file using mkswap command
  • Change /etc/fstab to point to the that file

Issue as below

  • Still wasting space if swap is not using
  • Hard to adjust size
  • Manual tasks involved

dphys-swapfile

The dphys-swapfile package can be installed to automate the tasks described above. It is not an entry in /etc/fstab, but a service.

  • Install dphys-swapfile package
  • Adjust config in /etc/dphys-swapfile
  • Enable dphys-swapfile service
  • Can run dphys-swapfile <swapon|swapoff> command

Issue as below

  • Still wasting space if swap is not using

zRAM

The zRAM module is installed by default, service is using systemd.

  • Check zram module available
modprobe zram
lsmod | grep zram
  • Add module and set module options
echo zram > /etc/modules-load.d/zram.conf
echo "options zram num_devices=1" > /etc/modprobe.d/zram.conf
  • Create zram0 device when booting by adding following line in /etc/udev/rules.d/99-zram.rules
KERNEL=="zram0", ATTR{disksize}="512M",TAG+="systemd"
  • Create systemd service file /etc/systemd/system/zram.service
[Unit]
Description=Swap with zram
After=multi-user.target

[Service]
Type=oneshot 
RemainAfterExit=true
ExecStartPre=/sbin/mkswap /dev/zram0
ExecStart=/sbin/swapon /dev/zram0
ExecStop=/sbin/swapoff /dev/zram0

[Install]
WantedBy=multi-user.target
  • Enable service, then reboot
sudo systemctl enable zram
  • Check swaps
cat /proc/swaps
swapon -s

Issue with zram

  • When memory not enough, then use swap space, but swap uses ram
  • It is the same solution as compress ram

References

How to enable the zRAM module for faster swapping on Linux

Exporting swap space on TrueNAS

Posted on by Bian Xi Leave a Comment on Exporting swap space on TrueNAS

Exporting swap space on TrueNAS

There are quite number of swap partitions on TrueNAS. In short, swap are mirror partitions on /dev/sdX1, which is 2GB for each mirror, data partitions are on /dev/sdX2.

As the top information, it has not been used, so just leave it until performance impacted.

Total Space

Following screen shows 4GB swap space in top command

top - 16:31:05 up  5:26,  4 users,  load average: 11.79, 11.36, 10.90
Tasks: 540 total,   1 running, 538 sleeping,   0 stopped,   1 zombie
%Cpu(s):  0.8 us,  9.4 sy,  0.0 ni, 46.1 id, 43.1 wa,  0.0 hi,  0.5 si,  0.0 st
MiB Mem :  32052.4 total,  13522.1 free,  17935.6 used,    594.7 buff/cache
MiB Swap:   4096.0 total,   4096.0 free,      0.0 used.  13739.1 avail Mem

Devices

There are two partitions as swap

truenas# swapon
NAME      TYPE      SIZE USED PRIO
/dev/dm-0 partition   2G   0B   -2
/dev/dm-1 partition   2G   0B   -3
truenas#

Partitions

DM info, shows /dev/dm-0 and /dev/dm-1 map to md127 and md126.

truenas# dmsetup ls
md127   (253:0)
md126   (253:1)
truenas# dmsetup info /dev/dm-0
Name:              md127
State:             ACTIVE
Read Ahead:        256
Tables present:    LIVE
Open count:        2
Event number:      0
Major, minor:      253, 0
Number of targets: 1
UUID: CRYPT-PLAIN-md127

truenas# dmsetup info /dev/dm-1
Name:              md126
State:             ACTIVE
Read Ahead:        256
Tables present:    LIVE
Open count:        2
Event number:      0
Major, minor:      253, 1
Number of targets: 1
UUID: CRYPT-PLAIN-md126

truenas#

MD info

Total 4 partitions involve, mirror into 2 raid1 devices.

Reported by proc

truenas# cat /proc/mdstat      
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md126 : active raid1 sde1[1] sdd1[0]
      2097152 blocks super non-persistent [2/2] [UU]

md127 : active raid1 sdc1[1] sdb1[0]
      2097152 blocks super non-persistent [2/2] [UU]

unused devices: <none>
truenas#

Reported by mdadm

truenas# mdadm --detail /dev/md127
/dev/md127:
           Version : 
     Creation Time : Wed Oct  6 11:08:56 2021
        Raid Level : raid1
        Array Size : 2097152 (2.00 GiB 2.15 GB)
     Used Dev Size : 2097152 (2.00 GiB 2.15 GB)
      Raid Devices : 2
     Total Devices : 2

             State : clean 
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : resync

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8       33        1      active sync   /dev/sdc1
truenas# mdadm --detail /dev/md126
/dev/md126:
           Version : 
     Creation Time : Wed Oct  6 11:08:57 2021
        Raid Level : raid1
        Array Size : 2097152 (2.00 GiB 2.15 GB)
     Used Dev Size : 2097152 (2.00 GiB 2.15 GB)
      Raid Devices : 2
     Total Devices : 2

             State : clean 
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : resync

    Number   Major   Minor   RaidDevice State
       0       8       49        0      active sync   /dev/sdd1
       1       8       65        1      active sync   /dev/sde1
truenas#

Block device info

Structure of partitions

truenas# lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda           8:0    0   1.4T  0 disk  
├─sda1        8:1    0     2G  0 part  
└─sda2        8:2    0   1.4T  0 part  
sdb           8:16   0   7.3T  0 disk  
├─sdb1        8:17   0     2G  0 part  
│ └─md127     9:127  0     2G  0 raid1 
│   └─md127 253:0    0     2G  0 crypt [SWAP]
└─sdb2        8:18   0   7.3T  0 part  
sdc           8:32   0 298.1G  0 disk  
├─sdc1        8:33   0     2G  0 part  
│ └─md127     9:127  0     2G  0 raid1 
│   └─md127 253:0    0     2G  0 crypt [SWAP]
└─sdc2        8:34   0 296.1G  0 part  
sdd           8:48   0 232.9G  0 disk  
├─sdd1        8:49   0     2G  0 part  
│ └─md126     9:126  0     2G  0 raid1 
│   └─md126 253:1    0     2G  0 crypt [SWAP]
└─sdd2        8:50   0 230.9G  0 part  
sde           8:64   0 298.1G  0 disk  
├─sde1        8:65   0     2G  0 part  
│ └─md126     9:126  0     2G  0 raid1 
│   └─md126 253:1    0     2G  0 crypt [SWAP]
└─sde2        8:66   0 296.1G  0 part  
sdf           8:80   1  14.9G  0 disk  
├─sdf1        8:81   1     1M  0 part  
├─sdf2        8:82   1   512M  0 part  
└─sdf3        8:83   1  14.4G  0 part  
zd0         230:0    0    20G  0 disk  
truenas#

zpool structure

List all zpool

truenas# zpool list
NAME        SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
boot-pool    14G  3.70G  10.3G        -         -     2%    26%  1.00x    ONLINE  -
pool0       296G  9.13G   287G        -         -     1%     3%  1.00x    ONLINE  /mnt
pool1      1.36T   383G  1009G        -         -    16%    27%  1.09x    ONLINE  /mnt
pool2      7.27T  1.12T  6.14T        -         -     2%    15%  1.10x    ONLINE  /mnt
pool3       230G  2.63G   227G        -         -     0%     1%  1.00x    ONLINE  /mnt
truenas#

For individual pool, can use following command find out partition info

truenas# zpool status pool0 -v
  pool: pool0
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
    The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
    the pool may no longer be accessible by software that does not support
    the features. See zpool-features(7) for details.
  scan: resilvered 600K in 00:00:03 with 0 errors on Mon Oct  4 04:49:30 2021
config:

    NAME                                      STATE     READ WRITE CKSUM
    pool0                                     ONLINE       0     0     0
      mirror-0                                ONLINE       0     0     0
        bf410fcf-2209-11ec-b8aa-001132dbfc9c  ONLINE       0     0     0
        bfcc498a-2209-11ec-b8aa-001132dbfc9c  ONLINE       0     0     0

errors: No known data errors
truenas#

find partition by id

zpool list doesn't have partition name, only got partition id, use following command to find out mapping partition id.

truenas# ls -l /dev/disk/by-partuuid
total 0
lrwxrwxrwx 1 root root 10 Oct  6 11:05 0e8d0027-65cc-4fa5-bb68-7d91668ca1f4 -> ../../sdf1
lrwxrwxrwx 1 root root 10 Oct  6 11:05 41ba87d7-2137-11ec-9c17-001132dbfc9c -> ../../sdb1
lrwxrwxrwx 1 root root 10 Oct  6 11:05 41cbb8fa-2137-11ec-9c17-001132dbfc9c -> ../../sdb2
lrwxrwxrwx 1 root root 10 Oct  6 11:05 5626c0ae-2137-11ec-9c17-001132dbfc9c -> ../../sdd1
lrwxrwxrwx 1 root root 10 Oct  6 11:05 563bbde1-2137-11ec-9c17-001132dbfc9c -> ../../sdd2
lrwxrwxrwx 1 root root 10 Oct  6 11:05 672278c8-92bc-4e99-8158-25e53eb085c9 -> ../../sdf2
lrwxrwxrwx 1 root root 10 Oct  6 11:05 757ce69e-207a-11ec-afcf-005056a390b2 -> ../../sda1
lrwxrwxrwx 1 root root 10 Oct  6 11:05 75827da1-207a-11ec-afcf-005056a390b2 -> ../../sda2
lrwxrwxrwx 1 root root 10 Oct  6 11:05 bf3063db-2209-11ec-b8aa-001132dbfc9c -> ../../sdc1
lrwxrwxrwx 1 root root 10 Oct  6 11:05 bf410fcf-2209-11ec-b8aa-001132dbfc9c -> ../../sdc2
lrwxrwxrwx 1 root root 10 Oct  6 11:05 bfb5835e-2209-11ec-b8aa-001132dbfc9c -> ../../sde1
lrwxrwxrwx 1 root root 10 Oct  6 11:05 bfcc498a-2209-11ec-b8aa-001132dbfc9c -> ../../sde2
lrwxrwxrwx 1 root root 10 Oct  6 11:05 e384f2ee-96dd-4b1b-ac68-8fe14ea92797 -> ../../sdf3
truenas#