Make the best of SSD+HDD in terms of storage and performance alltogether
- The problem: An SSD + HDD system can’t go faster than the slowest drive for every HDD (mostly data related) operations.
- A solution: Allows for one or more solid-state drives (SSDs) to act as a cache for slower rotational hard disk drives.
Some more details:
Think like this: you want to have a 4TB array, SSD of such size will set you back at least $10000, HDD RAID of similar size will cost you less than $500, even at RAID10 redundancy.
Problem is, that ’find’, or ’updatedb’ will easily take more than 10 minutes if you have large files (in the 100MB range) or few dozen minutes if you have smaller files on HDDs and at most a minute with the SSD.
Now, the only thing that needs to be read from such an array is metadata, which in itself is small, less than 1%.
If you could put only metadata on a SSD you’d get a disk just as fast in such workloads as the $10000 array for a fraction of the price.
In most small to medium businesses and home media servers you don’t need thousands of IOPS (which big database and large www servers need - that’s why SSD exclusive storage has its place), at the same time you want to have access to your most used files be fast (Windows roaming profiles, DE configuration files), and don’t have to manually move it between fast and slow storage.
Some references:
- ▻http://www.linux.com/learn/tutorials/754674-using-bcache-to-soup-up-your-sata-drives
SSDs are super fast but can be cost-prohibitive [while it’s the opposite for HDD]. With the help of bcache, you can use a smaller SSD as a caching drive for the larger, slower HDD. With this set up, you have the best of both worlds.
- A lightning fast SSD housing your operating system.
- A bcache-enabled SSD that caches for your large HDD data drive.
As of kernel 3.10, bcache is available with minimal installation and work.
Warning: Although you can set this up on an existing system (with existing data), I highly recommend you not do so.
Or check out g2p’s blocks, a conversion tool that enable bcache or LVM on existing block devices without moving data: ▻https://github.com/g2p/blocks
En Fr: Matériel : Accéleration disques durs via SSD sous Linux : les technos existantes (10/2012) ▻http://linuxfr.org/news/acceleration-ssd-sous-linux
Bcache For The Linux Kernel Might Finally Be Ready ▻http://www.phoronix.com/scan.php?page=news_item&px=MTI3NDg
An alternative to Bcache: SSD, LVM, Tiered storage - speeding up your storage - alpha version! ▻https://bbs.archlinux.org/viewtopic.php?id=113529
In my tests I saw some bottlenecks in LVM that made it impossible to achieve more than 300% gains (pure SSD setup was over 10 times faster) with mixed setup (HDD+SSD).
Commentaires et retours d’expérience bienvindus ;)