December 13, 201213 yr Yo, Has any1 tried to use a Hardware Raid card in conjunction with Unraid and use it as parity? For example an 4*1TB raid-5 for parity? This would speed-up parity calculations and better secure your array! gr33tz
December 13, 201213 yr Im using an ARC-1220 with 2x4TB drives. 4TB RAID0 for Parity and 1TB RAID1 for cache. I dont see how using RAID5 would be beneficial.
December 13, 201213 yr Author Im using an ARC-1220 with 2x4TB drives. 4TB RAID0 for Parity and 1TB RAID1 for cache. I dont see how using RAID5 would be beneficial. Raid-5 is still faster than a single disk for writing as data is written and spread over the disks in the raid-5 array, so parity calculations should be much faster! Another advantage is redundancy as you don't need to rebuild parity from scratch or even when used in raid-6 Dunno...just mindstorming here as I'm looking for faster parity calculations. Would be awesome if parity could be on a ZFS raidz array, no need for expensive hardware raid then! So suggestions welcome!
December 13, 201213 yr Im using an ARC-1220 with 2x4TB drives. 4TB RAID0 for Parity and 1TB RAID1 for cache. I dont see how using RAID5 would be beneficial. Raid-5 is still faster than a single disk for writing as data is written and spread over the disks in the raid-5 array, so parity calculations should be much faster! Another advantage is redundancy as you don't need to rebuild parity from scratch or even when used in raid-6 Dunno...just mindstorming here as I'm looking for faster parity calculations. Would be awesome if parity could be on a ZFS raidz array, no need for expensive hardware raid then! So suggestions welcome! Anything parity related is determined by MORE than just the parity drive. If you are writing to the array you will have TWO drives involved. The parity drive and the one the data is being written to. So your speed will be determined by the slowest of the two drives. If you are doing a sync or check then it will be determined by the slowest drive in the WHOLE array. The only time a faster parity makes sense is when you are writing to multiple array drives at the same time.
December 13, 201213 yr An uber-fast parity drive will have minimal impact on unRAID performance. I have done a 4x RAID-0 on an Areca 1882 for parity, and done a 2x RAID-0 with 256GB SSDs for parity, and both barely had any impact on parity protected writes to unRAID. You must have uber-fast parity AND data drives to get any significant speed benefit from such an arrangement. RAID-5 or RAID-0 parity only gives you a tiny additional margin of safety. Indeed, the parity drive is the LEAST important drive in the system.
December 13, 201213 yr Author I understand..now I'm getting 35MB/s write speed on a Hitachi Sata-3 7200rpm drive while normal write speeds are higher normally! Wouldn't speed be higher then using several disks at the same time? From experience have been using raidz in zfs and get write speeds of 119MB/s on 8*2TB raidz configuration! The only thing I was missing was the ease of adding more disks and creating more space like in Unraid!
December 14, 201213 yr You are getting good speeds with 35MB/s that is about what I get for writes on my arrays - depends on the drive in my arrays. The only way you will get much better with unRAID is if you make all of your drives SSDs. It is the trade off to using unRAID. You get slow writes because the raid scheme in unRAID is not stripped across multiple disks. Each disk has it's own file system and individual files are written to a single drive. For me that is the big advantage of unRAID to traditional raid schemes. If you loose more drives than the parity scheme supports at one time you DON'T loose your whole array. Just the data on the drives that died. When I had a hardware RAID-5 array I lost too much data when I lost multiple drives plus the card was extremely expensive besides. Another big benefit to this approach is that the drives can be spun down and only individual drives need to be spun up to access data from those disks. So you save money on the electric bill when the server stays on 24/7 - the drives aren't spinning 24/7 too. All that means that unRAID is very good for archival storage and not good for transactional servers that are always writing to the array and need the fastest read access possible real time.
December 14, 201213 yr The only time a faster parity makes sense is when you are writing to multiple array drives at the same time. I've tried fast parity drives with raid0 and hardware raid controllers also. It's only a small margin of improvement. Usually hardly worth the cost. If you get a caching controller and re-tune the kernel, you can burst at up to 55MB/s but it will slowly dwindle down to 35-40MB/s as you write more data. For lots of random writes with small files, the ARC-1200 RAID0/RAID1 hybrid works well and is cost effective. You can have a fast parity drive along with protected raid1 cache if you choose. (or application drive).
December 14, 201213 yr Author OK, I understand now! Thanks for all the advice and as several mentioned Unraid is more meant as an archive server! I'll be keeping my ZFS along side Unraid on ESXi. Hopefully one day ZFS will implement raid expansion (disk-per-disk basis) but doubt that as ZFS is meant for large clusters! It is possible (see: https://blogs.oracle.com/ahl/entry/expand_o_matic_raid_z) and more and more home users are asking for a disk-per-disk raid expantion! I owned 4 NAS before which had this feature but they had an expensive bay(bang)-for-buck problem! Synology for instance have an 12-bay NAS with raid expansion and Hybrid raid (use different sizes of disks like Unraid). Those are the features I'm looking for in a DIY build..and of course decent write speeds as it took about a week to copy my media from ZFS to Unraid! What a difference with Unraid 35MB/s...ZFS copy went @ 200MB/s+ gr33tz
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