32GB内存文件服务器缓存方案咨询（兼容Windows/Linux/FreeNAS）

Got it, let's tackle this. Since Windows Server 2012 R2 doesn't have native support for using system RAM as cache for storage pools, switching to either FreeNAS (now TrueNAS Core, but the core logic applies) or a Linux distro is your best bet. Below are tailored solutions for both platforms, leveraging your 32GB RAM, 4 HDDs, 1 SSD, and hot spare requirement:

FreeNAS uses ZFS, which natively leverages system RAM for read caching via the ARC (Adaptive Replacement Cache)—this is exactly what you need. Here's how to optimize it:

• ARC (RAM Cache): ZFS automatically uses idle system RAM for ARC by default. To ensure you leave enough RAM for the OS (say, 4GB), you can set a maximum limit for ARC:
  • Run this command temporarily: sysctl vfs.zfs.arc_max=29360128000 (this sets the max to 28GB, adjust if needed)
  • To make it permanent, add vfs.zfs.arc_max=29360128000 to /etc/sysctl.conf
• L2ARC (SSD Secondary Cache): Your SSD can act as a secondary cache for data that doesn't fit in ARC. To set this up:
  1. Open the web UI, go to Storage > Pools
  2. Select your existing pool, click Add VDEV
  3. Choose your SSD, set its type to Cache, then confirm
• Hot Spare: FreeNAS supports hot spares natively—you can add one during pool creation or later via the pool management menu by selecting a spare HDD and marking it as a hot spare.

Linux offers multiple ways to set up RAM + SSD caching for your storage pool. Here are the most reliable options:

1. ZFS on Linux (ZoL) #

Same ZFS logic as FreeNAS, but for generic Linux distros:

• First install ZFS utilities:
  • Debian/Ubuntu: apt install zfsutils-linux
  • RHEL/CentOS/Rocky Linux: dnf install zfs
• Create your pool with RAID-Z (choose RAID-Z1/2/3 based on redundancy needs), add the SSD as L2ARC, and include a hot spare:

  zpool create mypool raidz2 /dev/sdb /dev/sdc /dev/sdd /dev/sde cache /dev/sdf spare /dev/sdg
  

• Adjust ARC max RAM usage (28GB example):
  • Temporary: sysctl zfs.arc_max=29360128000
  • Permanent: Add zfs.arc_max=29360128000 to /etc/sysctl.d/90-zfs.conf

2. LVM Cache #

If you prefer LVM over ZFS, you can set up a combined RAM + SSD cache:

• Create a volume group with your HDDs and add a hot spare:

  pvcreate /dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdg
  vgcreate myvg /dev/sdb /dev/sdc /dev/sdd /dev/sde
  vgextend myvg /dev/sdg
  vgchange --addtag @spare myvg /dev/sdg
  

• Create a logical volume from the HDDs:

  lvcreate -l 100%FREE -n mylv myvg
  

• Set up a cache pool using the SSD, with 28GB allocated to RAM cache:

  lvcreate -L 100%FREE -n cache_pool myvg /dev/sdf
  lvconvert --type cache-pool --cachemode writeback --cache-settings memory.cache_size=28G myvg/cache_pool
  

• Attach the cache pool to your logical volume:

  lvconvert --type cache --cachepool myvg/cache_pool myvg/mylv
  

3. Bcache #

Bcache is a dedicated block-level caching tool for Linux:

• Install bcache tools:
  • Debian/Ubuntu: apt install bcache-tools
  • RHEL/CentOS/Rocky Linux: dnf install bcache-tools
• Create a RAID array with your 4 HDDs and add a hot spare:

  mdadm --create /dev/md0 --level=6 --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde
  mdadm /dev/md0 --add-spare /dev/sdg
  

• Initialize the SSD as a cache device and the RAID array as a backend device:

  make-bcache -C /dev/sdf
  make-bcache -B /dev/md0
  

• Attach the cache to the backend:

  echo $(cat /sys/block/bcache0/bcache/set_uuid) > /sys/block/bcache1/bcache/attach
  

• Set RAM cache size to 28GB (temporary; add to a systemd service or /etc/fstab for persistence):

  echo 28G > /sys/block/bcache1/bcache/cache_size
  

内容的提问来源于stack exchange，提问作者Hongkie