USING SSD AND HDD TOGETHER FULL

Both disks in the same pool means even higher chance of data loss (this is RAID0 after all) or corruption, additionally your performance will be sub par because of the different drive sizes and drive speeds.

USING SSD AND HDD TOGETHER FULL

You still detect errors, but you do not use the full capabilities of the system. With just a single disk, you give up on redundancy and self-healing.With ZFS, you have none of that, neither automatically nor manually, your data stays were it was written initially (or is already marked for deletion). What you are looking for is called a hybrid drive, for example Apple's Fusion Drive allows to fuse multiple disks together and automatically selects the storage location for every block based on access history (moving data is done when there is no load on the system or on rewrite). ZFS does no reshuffling of already written data.Although it is quite flexible, I think it is suboptimal for your current situation and goal, for the following reasons: ZFS is a file system designed for large arrays with many smaller disks. Is it a good idea to set up SSD + HDD in same pool, or is there a better way to optimize my pair of drives for both speed and capacity? While Marco's answer explained all the details correctly, I just want to focus on your last question/summary: Is it a good idea to set up SSD + HDD in same pool, or is there a better way to optimize my pair of drives for both speed and capacity?.If the SSD part of zpool is filled up, and I start accessing a bunch of data off HDD, and not so much off SSD, does ZFS make any effort to swap the hot data to SSD?.If the SSD part of zpool is filled up, does ZFS ever anticipate that I will have more writes soon and tries to move data from SSD to HDD in the background?.Does ZFS try to do anything smart with data shuffling once the SSD part of the zpool fill up? In particular,.How are writes distributed across the SSD and HDD when both are relatively empty?.ZFS obviously notices the difference in size between SSD and HDD partitions, but does ZFS automatically recognize the relative performance of SSD and HDD partitions? In particular,.Summary of questions if using SSD + HDD in a single zpool: If ZIL is on SSD and there is still plenty of room for more intents to be logged, does the ZIL still automatically get flushed to SSD? If so, when/under what circumstances?.Does data have to be copied from ZIL to L2ARC even if both are on same physical SSD?.Is L2ARC retained after system reboot, or does it have to be re-populated?.If I use SSD for L2ARC, is its capacity included in total available pool capacity, or is the pool capacity limited by HDD alone?.

If I set up SSD for ZIL + L2ARC, how hard is it to re-set it up with different partition sizes?.

Summary of questions if using SSD for ZIL + L2ARC: But what happens if I add a striped disk which effectively doubles my HDD speed (and capacity)? Doing this maximizes the size of L2ARC which is good. If I go the manually configured ZIL + L2ARC route, it seems like the ZIL only needs to be about (10 sec * HDD write speed) big. The ZIL should be automatically managed to be the right size and preferably live on the SSD as much as possible. Ideally, I would like to have ZFS transparently shuffle the data around behind the scenes to try to always keep the hot data on the SSD similarly to what L2ARC, and have a sensible amount of empty space on SSD for new writes.

But I don't know if everything is just going to the SSD for now, and everything will go to HDD later once SSD is all filled up. I have tried this, and noticed sustained read/write speeds greater than what HDD alone can muster. It also seems inefficient to have to copy data from ZIL to L2ARC if they are both on the same SSD, or even to HDD if there is currently no pressure on how much hot data I need on SSD.ДЄlternatively, it seems I can also just have 1 partition on SSD and 1 on HDD and add them to a zpool directly with no redundancy. Also it's not clear if the L2ARC is retained after system reboot or if it has to be populated again. What I don't like about it is that it's somewhat involved, potentially hard to reconfigure if I need to change the partitions, and it sounds like the maximum filesystem size is limited by the HDD alone since the intent is that everything on the ZIL and L2ARC has to also make it to disk, at least eventually. I have read that I can carve separate partitions into the SSD for the ZIL and L2ARC which would seem to do what I want, except I have to manually configure how big each partition should be. I am trying to get a well configured large, fast zpool out of it. So I have a desktop with a fast SSD and large HDD.

Using ssd and hdd together