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I've been building the full blockchain with geth. I resorted to using ZFS snapshots to recover from repeated failures caused by corrupted blocks according to geth reports. Whenever unrecoverable corruption was detected, I issued rollback in the hope that the corruption was recent and the process could continue. This worked for awhile but ultimately failed, and I assume this is because very early blocks are corrupt. So I've moved geth to another system in the hope that unreliable RAM was the cause of the trouble. I'm considering building a system with ECC RAM. But that is a side issue. To my question:

Now I'm observing progress on system 3 which seems to be doing well, albeit more slowly on HD instead of SSD as before, but I'm curious about a peculiarity seen with each sync attempt:

The snapshots below are named according to the block number that was complete at the time of the snapshot. I have adjusted the snapshot interval periodically so as to evenly space them out in terms of perceived work completed, or essentially, time. The curious part is the wildly varying ratios between of blockchain blocks logged vs. apparent space modified in the filesystem.

As most readers probably know, like most snapshot support, ZFS uses copy-on-write to preserve modified disk blocks. The space allocated to a snapshot is thus proportional to the dispersal of modification activity since the snapshot. This can be seen in the USED column of the zfs list report:

root@merle:/blockchain/eth# zfs list
NAME                             USED  AVAIL  REFER  MOUNTPOINT
naked3t                          586G  2.06T    19K  /naked3t
naked3t/blockchain               108G  2.06T    19K  /blockchain
naked3t/blockchain/eth           108G  2.06T  27.8G  /blockchain/eth
naked3t/blockchain/eth@2278805  2.56G      -  5.63G  -
naked3t/blockchain/eth@2598969  14.4G      -  24.5G  -
naked3t/blockchain/eth@2636231  14.4G      -  24.7G  -
naked3t/blockchain/eth@2675264  18.8G      -  25.0G  -
naked3t/blockchain/eth@2680721  20.9G      -  26.4G  -
naked3t/blockchain/eth@2682986  3.38G      -  27.8G  -

Note that geth apparently raced through ~37K blocks and required 14.4G of space to maintain the prior snapshot. But later, it slowed to a crawl, and I triggered a snapshot after only 2300 blockchain blocks, yet 20.9G had been consumed in maintaining the prior state to that point.

My questions are about what accounts for the differential, and to further explain, if this is predictable, as if there is something about the activity in certain period of the history that causes this, or if it is non-deterministic and I can expect to see different behavior if I were to restart the process. FWIW, the current slow period in process is around November, 2016.

Insights?

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    Someone else will flesh it out I imagine, but... spam attacks: blog.ethereum.org/2016/09/22/transaction-spam-attack-next-steps – Richard Horrocks Apr 9 '18 at 21:57
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    Basically this (extremely detailed) answer: ethereum.stackexchange.com/a/9892/52 – Richard Horrocks Apr 9 '18 at 21:59
  • Thanks. I vaguely recall reading about this event, although I thought it occurred in the spring. I take it that anyone who wishes to build their own full chain must reenact the entire play to assure integrity, and that we are tentatively stuck with this circumstance forever, in theory. I wish there was a way to download the blockchain from a trusted source to bypass this process. Some kind of a multi-signature attestation... – Bill Michaelson Apr 10 '18 at 13:22
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Commenters have answered my question adequately. Concise explanation is at Why is my node synchronization stuck/extremely slow at block 2,306,843?

  • Just a follow-up: It has been more than a week, but the machine finally broke through the clog sometime within the past 24 hours. I guesstimate that it started moving faster at around the early December, 2016 blocks. Since yesterday, it has zipped along and is now at around March, 2017. Posted for those in similar circumstance, wondering how long they will need to wait. – Bill Michaelson Apr 20 '18 at 13:33

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