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I am trying to find if the ZFS filesystem has added support for Trim to Raid 5? I am setting up an SSD array in Raid 5. I also would like to know if there is any good software raid 5 alternatives to an LSI raid controller card? Keep in mind, I am using ZFS on Ubuntu.

Nathan Sire
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    IMHO it is a little early to implement SSD RAID - the I in RAID is meant for Inexpensive! :-) - seriously, the benchmarks I've seen are not that encouraging compared to more established alternatives (like battery powered disk controller with lots of cache). – Paulo Scardine Sep 21 '12 at 20:18
  • I just found a great video. I learned that ZFS discourages use of a raid controller. http://www.youtube.com/watch?v=0Ug1qCXvZDg –  Sep 21 '12 at 20:27
  • So you are essentially saying to use a raid controller with flash memory for cache, similar to how one of these new pci express flash drives operate right off the pci bus lanes, which give giga bytes of read/write sequential speed? –  Sep 21 '12 at 20:29
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    1) In fact the large disks (several TB) could take so long to sync in a traditional RAID that you risk a second disk failing (fatal!); 2) No, IMHO you should use traditional disks with lots of cache unless you have and application where performance is above reliability (like large video processing); – Paulo Scardine Sep 21 '12 at 20:34
  • I see. I am going to setup a small amount of storage in raid 0 for compiling Java. 3 x 64 gig ssd's. So I am going for performance on that. And I will stick with traditional drives and raid 5 on my home lab server where I need long term storage for my repos etc... –  Sep 21 '12 at 20:47
  • I gotta agree with the others: don't use SSD for your RAIDs. RAID 5 uses striping which will deteriorate the performance of the SSDs quicker. Also, once you have 6 to 8 HDDs RAIDed together (RAID0 the fasted) they actually outperform the SSDs! You could get over 1 GB/s (that's 8Gb/s) read and write speeds with a good HW raid controller such as LSI MegaRAID - which also accepts an SSD card for caching. Hope this helps... –  Sep 21 '12 at 21:10
  • 1. This should be on SuperUser.com or ServerFault.com. 2. SSD have one major advantage over any mechanical drive: their low seek times. Unless you plan on regularly streaming data back and forth, the throughput of a mechanical drive is partially irrelevant, because it never gets the chance to reach it... – thkala Sep 22 '12 at 06:28

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TRIM and DISCARD support for ZFS is currently in alpha. Pawel Dawidek wrote the initial code for FreeBSD and Etienne Deschamps ported it to Linux.

For ZoL, you need to compile the experimental code yourself and set the zfs_notrim=0 option.

This feature will be disabled by default for a long while on most ZFS systems, but it exists and it works.

Darik Horn
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