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JRS Systems: the blog
Personal blog · jrs-s.netsystemsdata
JRS Systems: the blog is a personal blog at jrs-s.net about systems and data. Since 2015, 59 different Hacker News readers have linked it 64 times, most often “Will ZFS and non-ECC RAM kill your data?”. It is still writing: the last post was on 2026-10-15, and you can follow it by feed.
Rarely recommended · 4 of 40 sampled comments recommend it?
Why HN links it
HN readers link this blog to argue that ZFS does not need ECC RAM any more than other filesystems, and to recommend mirror vdevs over RAIDZ for easier expansion and faster resilvering.
- Recommended for · 4 comments
- Praised as a good article on mirror vdevs versus RAIDZ tradeoffs, one that made a commenter reconsider their ZFS practices.
Summarised by Claude from a sample of 40 HN comments that link here. Each comment is marked recommending, critical or neutral (citing without judging); how this works.
Most-linked posts?
- Will ZFS and non-ECC RAM kill your data?15 people · 16 mentions · first linked 2019-06-10
- Will ZFS and non-ECC RAM kill your data?11 people · 12 mentions · first linked 2015-07-22
- ZFS: Use mirror vdevs, not RAIDZ10 people · 10 mentions · first linked 2019-06-07
- /2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/9 people · 9 mentions · first linked 2016-01-12
- ZFS sync/async and ZIL/SLOG, explained4 people · 4 mentions · first linked 2019-05-02
- ZFS copies=n is not a substitute for device redundancy (2016)2 people · 2 mentions · first linked 2021-01-16
What Hacker News says?
https://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-y...
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “Synology reverses policy banning third-party HDDs”Submitted ZFS: Use mirror vdevs, not RAIDZ as a story · 115 points
HN discussionThe important key point is that you will not lose anything by using ZFS without ECC compared to using any other file system without ECC. The myth is that you specifically need ECC if you’ll be using ZFS, not that ECC is a really good idea for any file system. https://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-y...
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “The Synology End Game”Submitted ZFS copies=n is not a substitute for device redundancy (2016) as a story · 77 points
HN discussionRegarding ECC and ZFS: https://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-y... "Next, you read a copy of the same block – this copy might be a redundant copy, or it might be reconstructed from parity, depending on your topology. The redundant copy is easy to visualize – you literally stored another copy of the block on another disk. Now, if your evil RAM leaves this block alone, ZFS will see that the second…
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “Fujifilm Created a Magnetic Tape That Can Store 580 Terabytes”Submitted Verifying copies as a story · 41 points
HN discussion> It's possible to create the same amount of redundant storage space with only 6-8 hard drives with RAIDZ2 (RAID 6) redundancy. I've given up on striped RAID. Residential use requires easy expandability to keep costs down. Expanding an existing parity stripe RAID setup involves failing every drive and slowly replacing them one by one with bigger capacity drives while the whole array is in a degraded state and incurr…
Comment linking /2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
on “My 71 TiB ZFS NAS After 10 Years and Zero Drive Failures”Submitted ZFS sync/async and ZIL/SLOG, explained as a story · 5 points
HN discussionThat's not the case it mirrored vdevs. There is no degredatuon of the array with a failed drive in a mirrored vdev, it continues humming along perfectly fine. Also resilvers are not as intensive when rebuilding a mirror as you are just copying from one disk in the vdev to the other, not all X other drives and recalculating parity at the same time. This means less reads across the entire array and much much quicker r…
Comment linking /2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
on “Ceph: A Journey to 1 TiB/s”Submitted Rebalancing data on ZFS mirrors – JRS Systems: the blog as a story · 4 points
HN discussion> ZFS is nearly perfect but when it comes to expanding capacity it's just as bad as RAID. if you don't mind the overhead of a "pool of mirrors" approach [1], then it is easy to expand storage by adding pairs of disks! This is how my home NAS is configured. [1] https://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs...
Comment linking /2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
on “Ceph: A Journey to 1 TiB/s”Submitted Will ZFS and non-ECC RAM kill your data? as a story · 4 points
HN discussionI was curious about what a "nested" mirror is really. What exactly is nested? I'd setup a large pool with mirror vdevs, i.e. n sets of 2 disks per mirror. My half-remembered reasoning was that backups manage the risk you'll lose data. But replacing a disk in a mirror vdev is much easier, and faster, than doing so with RAIDZ. The risk of RAIDZ is that resilvering impacts multiple vdevs, is much more intensive than a…
Comment linking /2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
on “Btrfs has been deprecated in RHEL”Submitted Salter's Screwdriver Theory of Latency as a story · 3 points
HN discussionData that's about to be written to disk often resides in ram for some period of time - bit flips in non-ECC ram can silently corrupt the data before writing it out. ZFS doesn't prevent this though it might detect it with checksumming. https://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-y...
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “The Cheapest NAS”Submitted Will ZFS and non-ECC RAM kill your data? as a story · 3 points
HN discussionYou should always use mirrors! http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-... "don’t be greedy. 50% storage efficiency is plenty". Mirrors perform better, perform MUCH better when degraded, rebuild MUCH faster.
Comment linking /2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
on “ZFS Is the Best Filesystem For Now”Submitted About ZFS Recordsize as a story · 3 points
HN discussionHere is an article detailing how ZFS is virtually unaffected by random bit flips because it would have to occur in such a way as to cause a sha256 collision between one block and its parity block in order for it to repair a valid block with a corrupt one during a scrub. Furthermore it goes on to argue that only a highly specific large scale ram corruption could possibly cause corruption and by that time it's almost…
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “Should I buy ECC memory? (2015)”Submitted ZFS: Use mirror vdevs, not RAIDZ (2015) as a story · 2 points
HN discussionYou understand incorrectly. http://arstechnica.com/civis/viewtopic.php?f=2&t=1235679&p=2... http://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-yo... http://blog.brianmoses.net/2014/03/why-i-chose-non-ecc-ram-f... etc.
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “ZFS is the FS for Containers in Ubuntu 16.04”Submitted Will ZFS and non-ECC RAM kill your data? as a story · 2 points
HN discussionA quick google search brings up [0] telling ECC RAM is just as necessary as it is for another filesystem. [0]: http://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-yo...
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “FreeNAS: Open Source Storage Operating System”Submitted ZFS: Practicing failures on virtual hardware as a story · 2 points
HN discussionAgreed, mirror vdevs are the way to go. Here's a post that explains the tradeoffs between RAIDZ and mirror vdevs in great detail: http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-...
Comment linking /2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
on “FreeNAS: Open Source Storage Operating System”Submitted Adventures in Network Repair as a story · 1 points
HN discussionThanks for catching that - my statement was definitely too strong in implying data invulnerability. I was hinting that you still get a bit of extra protection with ZFS over other filesystems, both on Non-ECC RAM. There is a chance with a stuck/corrupt bit that checksum will fail and you will get a read error. I interpreted OP as saying ECC is a must for ZFS, but I don't think you are more prone to corruption that an…
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “Best CPUs for Workstations: 2017”Submitted Use mirror vdevs, not RAIDZ. (2015) as a story · 1 points
HN discussion> [...] because it runs ZFS, which basically doesn't work unless you have ECC memory. That's a misconception, to quote Matthew Ahrens, cofounder of ZFS: "There's nothing special about ZFS that requires/encourages the use of ECC RAM more so than any other filesystem." See also [0]. [0] http://jrs-s.net/2015/02/03/will-zfs-and-non-ecc-ram-kill-yo...
Comment linking /2015/02/03/will-zfs-and-non-ecc-ram-kill-your-data/
on “Best CPUs for Workstations: 2017”Submitted ZFS sync/async and ZIL/SLOG, explained as a story · 1 points
HN discussion
