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seen Apr 10 at 15:46

Mar
25
awarded  Yearling
Feb
6
answered OpenVPN clients traffic
Jan
9
awarded  Nice Answer
Dec
2
awarded  Famous Question
Sep
24
awarded  Popular Question
Jun
15
comment Is KVM stable enough for production use in 2011?
@JoelESalas: Live migration is possible with dual primary mode, but I do not use that. I assume DRBD protocol C is mandatory in that scenario. DRBD behaves much like shared storage in dual primary. I have LVM below DRBD and create one DRBD pair per VM disk. With LVM on top, use LVM cluster support.
Jun
11
comment Is KVM stable enough for production use in 2011?
@JoelESalas: I currently prefer DRBD below the VMs and cache=none. cache=writethrough was bad advice actually, and it is not default anymore. cache=writeback is OK for low IO machines, but heavy writers gain problems with it, so cache=none is best option now.
May
15
comment KVM guest io is much slower than host io: is that normal?
cache=writeback does not add any real-life risks (important data is not in danger, only in-flight data, which is discarded on crash anyways). Only cache=unsafe does. Writeback does not imply additional hardware requirements ("battery backed RAID array" does not help in any way). It has the same integrity level as an HDD write-cache: both are flushed when necessary by the operating system.
Apr
23
comment What are the risks of running a database on a server without ECC RAM?
For MySQL (InnoDB), a flipping bit causes a 16KB page checksum to be invalid. Because MySQL just dies encountering such errors in index or data, it will enter a restart loop, crashing again whenever the block is encountered again. You may start in a recovery mode and try to dump all data, hoping it was an index page, but it's risky because data may be corrupt. Put simply: A bit flip in InnoDB data means restore from backup. All of it. Happened to me last week - easy to replace slave DB. Non-ECC RAM is a very bad idea for databases, and a bad idea in general, also desktops with current sizes.
Apr
12
awarded  Popular Question
Apr
3
comment How does BTRFS compare to ZFS?
@Ysangkok: Thanks for the update, I'm actually using ZOL for quite some time now (RCs) and am impressed by the snapshot performance. Very good to have DKMS packages for Debian, I think I will deploy it on a few more systems.
Mar
25
awarded  Yearling
Oct
21
awarded  Revival
Oct
11
comment Is current SATA 6 gb/s equipment simply unreliable?
Also, two different controllers (LSI) tested. I think I have now replaced everything except the disks :-)
Oct
8
comment Copying a large directory tree locally? cp or rsync?
Checksumming is done on files that differ at the size and timestamp check. If you're paranoid (like after a power outage during copy) you can force checksumming on all files, but on a local transfer, that's usually slower than starting from scratch.
Oct
8
comment Copying a large directory tree locally? cp or rsync?
actually, rsync detects local transfers and enables whole-file copy without checksumming automagically.
Oct
8
comment Any experience with SATA SAS Interposer Cards?
Thanks for the additional insight on this topic. Perhaps you can shed some light on my original problem, which is hidden in the comments: I have some SAS backplanes with SATA disks and Adaptec 5 and 6 series controllers and disks tend to simply drop out of the array. Power-cycle and they reappear, no flaws recorded in SMART values. I have since disabled NCQ on one of the arrays and it seems to help. But it appears as a mystery to me why these SATA drives (desktop class, granted) create such conflicts.
Oct
8
comment Is current SATA 6 gb/s equipment simply unreliable?
Can't keep the cable theory up since it also happens on a second array and with expensive brand cables (external). It's focused on the rear backplanes as it seems, not all disks per se. So a disk / SAS switch compatiblity issue?
Oct
8
comment Do SATA disks on an SAS backplane impose cable length limits?
Actually my idea of cable length issues was very wrong from the beginning: the rear backplane has shorter cabling than the front backplane. I can't test much on these in-production arrays right now, but I can rule out bad cables because in total 4 internal and 4 external cables were tested. Must be a hard drive incompatibility.
Oct
4
accepted Do SATA disks on an SAS backplane impose cable length limits?