SSD cache device to a software RAID5 using LVM2

Continuing our series LVM2 plus cache device:

  1. single hard disk with a SSD device SSD cache device to a hard disk drive using LVM, which uses SSD drive as a cache device to a single hard drive.
  2. Mirror LVM2 device with a SSD device for cache – SSD cache device to a software raid using LVM2 – software mirror across two devices with an additional SSD cache device over the mirror.

And now we show you how to do software RAID5 with SSD cache nvme using LVM2.

The goal:
Caching RAID5 consisting of three 8T hard drives with a single 1T NVME SSD drive. Caching reads, i.e. the write-through is enabled ().
Our setup:

  • 1 NVME SSD disk Samsung 1T. It will be used for writethrough cache device (you may use writeback, too, you do not care for the data if the cache device fails)!
  • 3 Hard disk drive 8T grouped in RAID5 for redundancy.

Keep on reading!

SSD cache device to a software raid using LVM2

Inspired by our article – SSD cache device to a hard disk drive using LVM, which uses SSD driver as a cache device to a single hard drive, we decided to make a new article, but this time using two hard drives in raid setup (in our case RAID1 for redundancy) and a single NVME SSD drive.
The goal:
Caching RAID1 consisting of two 8T hard drive with a single 1T NVME SSD drive. Caching reads and writes, i.e. the write-back is enabled.
Our setup:

  • 1 NVME SSD disk Samsung 1T. It will be used for writeback cache device (you may use writethrough, too, to maintain the redundancy of the whole storage)!
  • 2 Hard disk drive 8T grouped in RAID1 for redundancy.

STEP 1) Install lvm2 and enable the lvm2 service

Only this step is different on different Linux distributions. We included three of them:
Ubuntu 16+:

sudo apt update && apt upgrade -y
sudo apt install lvm2 -y
systemctl enable lvm2-lvmetad
systemctl start lvm2-lvmetad

CentOS 7:

yum update
yum install -y lvm2
systemctl enable lvm2-lvmetad
systemctl start lvm2-lvmetad

Gentoo:

emerge --sync
emerge -v sys-fs/lvm2
/etc/init.d/lvm start
rc-update add default lvm

Keep on reading!

aptly mirror: ERROR: unable to update: no candidates for debian-installer/binary-amd64/Packages found

Always check the source what supports when trying to mirror! We have lost some time before discovering that our source repository does not support udeb and source packages! If you create a mirror with “-with-sources=true -with-udebs=true” the update process will require files, which may not exists in the source repository if it does not offer udeb or source files and you’ll end up with broken mirror and error for missing file!

Downloading & parsing package files...
Downloading http://aptly.example.com/ubuntu/dists/xenial-myrepos/main/binary-amd64/Packages.bz2...
ERROR: unable to update: no candidates for http://aptly-master.example.com/ubuntu/dists/xenial-myrepo/main/debian-installer/binary-amd64/Packages found

If you get error for “debian-installer/binary-amd64/Packages” not found, check the source repository if it offers udeb and/or source packages – probably not, so drop your mirror and recreate it including one or the two options

-with-sources=false -with-udebs=false

Keep on reading!

aptly mirror – gpgv: Can’t check signature: public key not found

If you want to mirror repositories from your current aptly server to a new server you must import the GPG key from your old server because you are going to encounter the following error:

gpgv: Signature made Fri 22 Apr 2019 17:35:04 AM UTC using DSA key ID FDC7A25E
gpgv: Can't check signature: public key not found

Looks like some keys are missing in your trusted keyring, you may consider importing them from keyserver:

gpg --no-default-keyring --keyring trustedkeys.gpg --keyserver pool.sks-keyservers.net --recv-keys 181482CCFDC7A25E

Sometimes keys are stored in repository root in file named Release.key, to import such key:

wget -O - https://some.repo/repository/Release.key | gpg --no-default-keyring --keyring trustedkeys.gpg --import

ERROR: unable to fetch mirror: verification of detached signature failed: exit status 2

And the mirror command fails. The problem is

you must import the GPG key from your old server in trustedkeys.gpg (even if you have already imported it in the new server with apt-key!!!)

Here is how to list, export and import it (we are going to import it in default and trustedkeys.gpg, because it is more convenient, but it is not mandatory to be in the default).
Keep on reading!