Disk spindown on dedicated iSCSI disk.

[clement]

Hi, I'm a happy user of two FreeNAS servers for a few years now, on one of them I'm a little bit on the edge in terms of storage.
I have a 7200rpm 500to HDD laying around that I was thinking of using just for my iSCSI virtual disk, keeping it off the main ZFS pool to get some extra space in it.
With my networking I think I could benefit the extra speed compared to the 5400rpm main pool. However noise does matter as the server is in the same room as where I sleep, and I was thinking about using the slowdown and acoustic level option that I never used yet in FreeNAS.

What do you think about those ? And also if there's no replication or snapshots on this pool, is there anything from FreeNAS that could wake the disk regularly ?
The idea is that the disk would spin up only when I'm actually using my main computers connected to the iSCSI, would that work ? And does it really affect disk if it's just one or 2 spin up/down a day ?

Thanks

 

[nightshade00013]

You are better off not using iSCSI at all if you are going to put the data on only one disk. One of the big problems is while you are using a drive that is 500GB in size you would actually only be able to effectively use a little less than half of it for iSCSI since the system doesn't know what the data is underneath. The only advantage you could gain from something like this is the ability to replicate and snapshots and even then you are limiting a lot of things since the drive is not a part of a pool. Otherwise the other advantage I could really see of doing this is over time adding more disks so that you can mirror the original and then add more vDev's to the iSCSI pool. If you are not planning to do those things then just install it in a computer and then do backups to the FreeNAS pool.

And as far as the other pool being slower well that depends on the number of disks involved but in simple terms a pool of let's say seven 5400 rpm drives in a RaidZ2 the 7200 rpm disk will be slower.

https://calomel.org/zfs_raid_speed_capacity.html

In all honesty raw speed wise a pool with 7 drives in a RaidZ2 even with all the drives at 5400 rpm would be faster than your average consumer SSD the point where the SSD would be faster is when lots of IOPS are needed.

Could you let the drive power down, sure. Will it be detrimental to the drive.... basically be no different than it living in a local pc. And if noise is an issue because the FreeNAS is in your bedroom installing the drive in a local pc eliminates another perceived issue.

 

[clement]

Thanks for your advise, I'm using 3 disks in raidZ1 on my main zfs pool and tought this setting was making me lose a lot of write speed, but not that much according to your link.
The reason why I was thinking about throwing that disk in the NAS is that I need to have the same data accessible from 3 different computers around the house. Also, it's not that I don't care at all about the data that will be in this disk, but not more than the regular datas I have on my computers and I don't back them up, so not being able to use snapshots or replication isn't an issue (compared to my zfs pool that I really don't want to lose because of disk failures).

Also, I didn't fully understand, why I could only use half of the 500GB in this configuration ?
If that's the case indeed I'm better off actually buying more disks and expending my zfs pool

 

[nightshade00013]

iSCSI is not aware of what is on the disk so the way FreeNAS handles things makes it very bad to use the whole drive. You can actually read a little about it here https://doc.freenas.org/9.3/freenas_sharing.html?highlight=iscsi#extents

But basically once the disk is ZFS formatted you will lose a percentage for the filesystem. After that you should only use 50% of that or your storage will suffer performance issues.

So basically by using the disk in FreeNAS via iSCSI you are turning a 500GB disk into a much smaller disk.