let's say 16G cause we have 16G of actual RAM - but it's really up to you to decide that) and choose to leave it unformatted. "Add GPT Partition" on the 1st disk, give it the same or half the size of your RAM (e.g.
#HOW TO DIVIDE DISKS IN SOFTRAID SOFTWARE#
In the end, if you have a choice, get a lower cache in favor of a higher spin rate.Looking to create a Software RAID 1 setup for your 2-disk server on Ubuntu Server 20.04? On the other hand, if you, your software, or your (non-existent at the moment) RAID array disables the drive cache, you paid a lot of money for nothing. If you're particularly IO driven, you'll see an improvement. After you add enough spindles, the disk stops being the bottleneck, and it becomes the transit to the array (you're not there yet, don't worry).Įssentially, more cache gives you more wiggle room when it comes to dumping a lot of data on the disk(s). So with a RAID system, you have several disks that are being fed, thus increasing the IOPS. At the point the cache fills up, your computer waits on the disk to clear the "dirty" data (data that needs written). If you keep hammering it, it keeps feeding into cache.
If you feed the hard drive more data than it can put on a disk, then it uses cache. Each of your disk's spindles has a statistic called IOPS (I/O Operations Per Second - ) that determines how fast it can put bits on the spinning platters. The performance will really depend on the load that you're putting on the disks and where the bottleneck lies. Storing things in memory is really cheap. In other words, actually putting things on disk is expensive, in terms of time. SATA Disks that handle write caching properly?Īnyway, in response to your question.more drive cache gives the drive more space to "play" with. These questions have some interesting reading: I would read Question 9 under "Setup Considerations" in the Software RAID HOWTO: Additional software may be available to do this). There's no NVRAM that keeps the data, and the disks don't keep spinning thanks to a battery backup (on their own, anyway. If the drives have said "ok, we've got the data", and then the power dies while the data is still in cache, there's a problem. Software RAID doesn't really have that sort of option. The battery exists to either write the data to NVRAM, in the event of a controller, or to the physical disks, in the event of a battery-backed array. This causes bad things in software that really needs to know data exists on the disk. Cache helps the performance at the expense of reliability, because if the power dies, your cache goes away, even though the software thought it was safe.
The reason is that RAID is typically designed to ensure that your data is safe, and to increase performance. Cache and RAID has an interesting relationship.Įxpensive RAID controllers have built-in cache, and they turn the drive cache off (typically).