Tag Archives: xfs

Adding a swapfile on the fly as a temporary solution for a Server with few memory

Here is an easy trick that you can use for adding swap temporarily to a Server, VMs or Workstations, if you are in an emergency.

In this case I had a cluster composed from two instances running out of memory.

I got an alert for one of the Servers, reporting that only had 7% of free memory.

Immediately I checked it, but checked also any other forming part of the cluster.

Another one appeared, had just only a bit more memory than the other, but was considered in Critical condition too.

The owner of the Service was contacted and asked if we can hold it until US Business hours. Those Servers were going to be replaced next day in US Business hours, and when possible it would be nice not to wake up the Team. It was day in Europe, but night in US.

I checked the status of the Server with those commands:

# df -h

There are 13GB of free space in /. More than enough to be safe as this service doesn’t use much.

# free -h
              total        used        free      shared  buff/cache   available
Mem:           5.7G        4.8G        139M        298M        738M        320M
Swap:            0B          0B          0B

I checked the memory, ok, there are only 139MB free in this node, but 738MB are buff/cache. Buff/Cache is memory used by Linux to optimize I/O as long as it is not needed by application. These 738 MB in buff/cache (or most of it) will be used if needed by the System. The field available corresponds to the memory that is available for starting new applications (not counting the swap if there was any), and basically is the free memory plus a fragment of the buff/cache. I’m sure we could use more than 320MB and there is a lot if buff/cache, but to play safe we play by the book.

With that in mind it seemed that it would hold perfectly to Business hours.

I checked top. It is interesting to mention the meaning of the Column RES, which is resident memory, in other words, the real amount of memory that the process is using.

I had a Java process using 4.57GB of RAM, but a look at how much Heap Memory was reserved and actually being used showed a Heap of 4GB (Memory reserved) and 1.5GB actually being used for real, from the Heap, only.

It was unlikely that elastic search would use all those 4GB, and seemed really unlikely that the instance will suffer from memory starvation with 2.5GB of 4GB of the Heap free, ~1GB of RAM in buffers/cache plus free, so looked good.

To be 100% sure I created a temporary swap space in a file on the SSD.

# fallocate -l 1G /swapfile-temp

# dd if=/dev/zero of=/swapfile-temp bs=1024 count=1048576 status=progress
1034236928 bytes (1.0 GB) copied, 4.020716 s, 257 MB/s
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 4.26152 s, 252 MB/s

If you ask me why I had to dd, I will tell you that I needed to. I checked with command blkid and filesystem was xfs. I believe that was the reason.

The speed writing to the file is fair enough for a swap.

# chmod 600 /swapfile-temp

# mkswap /swapfile-temp
Setting up swapspace version 1, size = 1048572 KiB
no label, UUID=5fb12c0c-8079-41dc-aa20-21477808619a

# swapon /swapfile-temp

I check that memory is good:

# free -h
              total        used        free      shared  buff/cache   available
Mem:           5.7G        4.8G        117M        298M        770M        329M
Swap:          1.0G          0B        1.0G

And finally I check that the Kernel parameter swappiness is not too aggressive:

# sysctl vm.swappiness
vm.swappiness = 30

Cool. 30 is a fair enough value.

Installing Red Hat Linux in a M.2 that crashes the installer

Few months ago I encountered with a problem with RHEL installer and some of the M.2 drives.

I’ve productized my Product, to be released with M.2 booting SATA drives of 128GB.

The procedure for preparing the Servers (90 and 60 drives, Cold Storage) was based on the installation of RHEL in the M.2 128GB drive. Then the drives are cloned.

Few days before mass delivery the company request to change the booting M.2 drives for others of our own, 512 GB drives.

I’ve tested many different M.2 drives and all of them were slightly different.

Those 512 GB M.2 drives had one problem… Red Hat installer was failing with a python error.

We were running out of time, so I decided to clone directly from the 128GB M.2 working card, with everything installed, to the 512 GB card. Doing that is so easy as booting with a Rescue Linux USB disk, and then doing a dd from the 128GB drive to the 512GB drive.

Booting with a live USB system is important, as Filesystem should not be mounted to prevent corruption when cloning.

Then, the next operation would be booting the 512 GB drive and instructing Linux to claim the additional space.

Here is the procedure for doing it (note, the OS installed in the M.2 was CentOS in this case):

Determine the device that needs to be operated on (this will usually be the boot drive); in this example it is /dev/sdae

# df -h 
Filesystem                             Size  Used Avail Use% Mounted on
/dev/mapper/centos_4602c-root           50G  2.4G   47G   1% /
devtmpfs                                16G     0   16G   0% /dev
tmpfs                                   16G     0   16G   0% /dev/shm
tmpfs                                   16G  395M   16G   3% /run
tmpfs                                   16G     0   16G   0% /sys/fs/cgroup
/dev/sdae1                            1014M  146M  869M  15% /boot
/dev/mapper/centos_4602c-home           57G   33M   57G   1% /home
tmpfs                                  3.2G     0  3.2G   0% /run/user/0
logs                                    68G  7.4M   68G   1% /logs
mysql                                  481G  128K  481G   1% /mysql
N58-C3-D16-P3-S1                       491T  334G  490T   1% /N58-C3-D16-P3-S1

Extend the OS partition using Parted

# parted /dev/sdae
print
resizepart PART_NUMBER END
quit

Where:

  • PART_NUMBER: Is the partition number obtained from the “print” command
  • END: This is the end of the drive; for example, for a 50GB drive, enter 50000

Examining the LVM Partitions

The centos_4602c-root LVM partition is the one we want to extend.

# lsblk /dev/sdae
NAME                          MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sdae                           65:224  0   477G  0 disk 
├─sdae1                        65:225  0     1G  0 part /boot
└─sdae2                        65:226  0 475.9G  0 part 
  ├─centos_4602c-root         253:0    0    50G  0 lvm  /
  ├─centos_4602c-swap         253:1    0  11.9G  0 lvm  [SWAP]
  └─centos_4602c-home         253:2    0  56.3G  0 lvm  /home

Using LVM Commands

The following commands will:

  • Display the LVM volumes on the system
  • Resize a volume (device)
  • Re-display the updated LVM volumes
  • Extend the desired LVM partition (lvextend command)
# pvdisplay
  /dev/sdbm: open failed: No medium found
  /dev/sdbn: open failed: No medium found
  /dev/sdbj: open failed: No medium found
  /dev/sdbk: open failed: No medium found
  /dev/sdbl: open failed: No medium found
  --- Physical volume ---
  PV Name               /dev/sdae2
  VG Name               centos_4602c
  PV Size               118.24 GiB / not usable 3.00 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              30269
  Free PE               0
  Allocated PE          30269
  PV UUID               yvHO6t-cYHM-CCCm-2hOO-mJWf-6NUI-zgxzwc
# pvresize /dev/sdae2
  /dev/sdbm: open failed: No medium found
  /dev/sdbn: open failed: No medium found
  /dev/sdbj: open failed: No medium found
  /dev/sdbk: open failed: No medium found
  /dev/sdbl: open failed: No medium found
  Physical volume "/dev/sdae2" changed
  1 physical volume(s) resized or updated / 0 physical volume(s) not resized
# pvdisplay
  /dev/sdbm: open failed: No medium found
  /dev/sdbn: open failed: No medium found
  /dev/sdbj: open failed: No medium found
  /dev/sdbk: open failed: No medium found
  /dev/sdbl: open failed: No medium found
  --- Physical volume ---
  PV Name               /dev/sdae2
  VG Name               centos_4602c
  PV Size               <475.84 GiB / not usable 3.25 MiB
  Allocatable           yes 
  PE Size               4.00 MiB
  Total PE              121813
  Free PE               91544
  Allocated PE          30269
  PV UUID               yvHO6t-cYHM-CCCm-2hOO-mJWf-6NUI-zgxzwc
# vgdisplay
  --- Volume group ---
  VG Name               centos_4602c
  System ID             
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  6
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               3
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               <475.93 GiB
  PE Size               4.00 MiB
  Total PE              121838
  Alloc PE / Size       30269 / <118.24 GiB
  Free  PE / Size       91569 / 357.69 GiB
  VG UUID               ORcp2t-ntwQ-CNSX-NeXL-Udd9-htt9-kLfvRc
# lvextend -l +91569 /dev/centos_4602c/root 
  Size of logical volume centos_4602c/root changed from 50.00 GiB (12800 extents) to <407.69 GiB (104369 extents).
  Logical volume centos_4602c/root successfully resized.

Extend the xfs file system to use the extended space

The xfs file system for the root partition will need to be extended to use the extra space; this is done using the xfs_grow command as shown below.

# xfs_growfs /dev/centos_4602c/root  
meta-data=/dev/mapper/centos_4602c-root isize=512    agcount=4, agsize=3276800 blks
         =                       sectsz=512   attr=2, projid32bit=1          =                       crc=1        finobt=0 spinodes=0 data     =                       bsize=4096   blocks=13107200, imaxpct=25 
         =                       sunit=0      swidth=0 blks 
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1 log      =internal               bsize=4096   blocks=6400, version=2          =                       sectsz=512   sunit=0 blks, lazy-count=1 
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 13107200 to 106873856 

Verify the results

Note that the c-root LVM partition is now 408GB.

# df -h 
Filesystem                             Size  Used Avail Use% Mounted on
/dev/mapper/centos_4602c-root          408G  2.4G  406G   1% /
devtmpfs                                16G     0   16G   0% /dev
tmpfs                                   16G     0   16G   0% /dev/shm
tmpfs                                   16G  395M   16G   3% /run
tmpfs                                   16G     0   16G   0% /sys/fs/cgroup
/dev/sdae1                            1014M  146M  869M  15% /boot
/dev/mapper/centos_4602c-home           57G   33M   57G   1% /home
tmpfs                                  3.2G     0  3.2G   0% /run/user/0
logs                                    68G  7.4M   68G   1% /logs
mysql                                  481G  128K  481G   1% /mysql
N58-C3-D16-P3-S1                       491T  334G  490T   1% /N58-C3-D16-P3-S1

So now we are able to clone directly from one 512GB to another.

You may be interested to take a look to the commands:

growpart
resize2fs
xfs_growfs (from xfsprogs package)

If you want to do this in an instance in Amazon, here is a very good documentation.