iSCSI Storage Performance

[olaex]

Hello

I am going to plan a NAS and iSCSI storage for an VMWARE ESXi.

The Freenas Server will have the following hardware:
- AMD 4 Core Processor ~2,3 GHz
- 8GB ECC RAM
- 3 1,5 TB 7200rpm hard drives

The freenas server will only be used to store files and make backups. The iSCSI storage will be used for about ~3 VMs.

But i have the following question. Which filesystem should i use? Und what RAID System? With 3 HDDs i think Raid5 would be useful.

Does andybody have experiences with 3 HDDs and their performance?

Thank you

 

[jgreco]

You want performance? You'll mirror two drives together and use that for iSCSI. Personally I don't see a ton of benefits to ZFS for that, and ZFS performance isn't always what you'd expect with iSCSI, especially if the disk supports lots of writes or you want to use more than a terabyte of the 1.5TB, so if it were me, I'd mirror two drives together with UFS and use it for a 1.5TB iSCSI vmfs filesystem. You take the other drive and use it for backups. Note that if you're planning to use something like ghettoVCB over NFS, NFS on FreeNAS with ESXi may require a ZIL in order to have acceptable write performance. So you make that another iSCSI extent, mount it separately on ESXi, and run backups to it....

 

[olaex]

I don not know the performance of freenas and zfs. what is the typical write and read performance with zfs and 3 HDDs?
i only want to build a second nas with old hardware and i do not want do buy another harddrives and raid controller for the esxi, so i thought, i could use the freenas server for the esxi too.

with backups i mean my personal data. and not the ESXi. but if i have time during the holidays i think i would try this too. i do not really know ghettoVCB or something else.

 

[jgreco]

We don't know the performance of FreeNAS on your specific hardware either. It can be dependent on many things. However, RAIDZ (what you'd use for 3 drives) requires you to use ZFS, and it has some performance implications. First, it's slower, because it's a bit like RAID5. Mirrored drives are very likely to be faster. Second, ZFS needs to be tuned to behave nicely with a "slow" ZFS storage pool, which yours would be. It might seem to be working all very nicely for you and then one day when you go at it with some sustained writes during a scrub, it all goes to hell and ESXi freaks and your datastore goes all insane.

So the word of advice from those of us who have done it: you CAN use ZFS for iSCSI and you CAN make it work well, but it needs to be designed and tested rather carefully. ZFS with mirroring results in a faster pool than a 3-disk RAIDZ, so that's a major win to go with mirroring. It is still likely to need other tuning though.

Or you can use UFS which only offers mirroring. And you won't need to tune.

So the solution I outlined assumes you want some data protection for your VM's and no data protection for your backups (because, well, they're backups). That could be wrong of course, but seems like the best case scenario to me.