I have an old system (only the hardware, it runs –current) which reboots itself from time to time (mostly during the daily periodic(8) run, but also during a lot of compiling (portupgrade)). There is no obvious reason (no panic) why it is doing this. It could be that there is some hardware defect, or something else. It is not important enough to get a high enough priority that I try hard to analyze the problem with this machine. The annoying part is, that sometimes after a restart apache does not start. So if this happens, the solution is to login and start the webserver. If the webserver would start each time, nearly nobody would detect the reboot (root gets an EMail on each reboot via an @reboot crontab entry).
My pragmatic solution (for services started via a good rc.d script which has a working status command) is a crontab entry which checks periodically if it is running and which restarts the service if not. As an example for apache and an interval of 10 minutes:
*/10 * * * * /usr/local/etc/rc.d/apache22 status >/dev/null 2>&1 || /usr/local/etc/rc.d/apache22 restart
For the use case of this service/machine, this is enough. In case of a problem with the service, a mail with the restart output would arrive each time it runs, else only after a reboot for which the service did not restart.
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I am tired of bad network cards on mainboards. Can someome who knows a marketing guy of a mainboard manufacturer please please tell them to integrate a good network card (Intel ones comes to my mind, but other non-RealTec ones are not bad either… if an Intel one is not possible at all)? They just need to sell those mainboards as gaming and/or multimedia optimized:
- a good network card transfers more data per second (even while the CPU is used much)
- a good network card does not take much CPU (good DMA engine and some IP-stuff-in-hardware features)
Similar things can be told about good/bad SATA controllers and USB controllers. If done right, they affect the system less and/or perform better than not so good parts.
Yes, most of this does not affect gaming in a significant way, but a lot of other hardware gamers buy does not affect the gaming significantly.
The point is, that they are willing to give more money to get something better. So please, give them the possibility to pay a little bit more for good quality so that good stuff will go mainstream.
And do not underestimate the power of mouth-to-mouth marketing. If you produce something better than other companies for a fair price (no need to play the we-are-the-cheapest game, just take care to not be the most expensive one), it will be bought.
BTW: This is similar to the marketing with good capacitors, just on an IT instead of an electrical level.
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Currently I play a little bit around with my ZFS setup. I want to make it faster, but I do not want to spend a lot of money.
The disks are connected to an ICH 5 controller, so an obvious improvement would be to either buy a controller for the PCI slot which is able to do NCQ with the SATA disks (a siis(4) based one is not cheap), or to buy a new system which comes with a chipset which knows how to do NCQ (this would mean new RAM, new CPU, new MB and maybe even a new PSU). A new controller is a little bit expensive for the old system which I want to tune. A new system would be nice, and reading about the specs of new systems lets me want to get a Core i5 system. The problem is that I think the current offers of mainboards for this are far from good. The system should be a little bit future proof, as I would like to use it for about 5 years or more (the current system is somewhere between 5–6 years old). This means it should have SATA-3 and USB 3, but when I look at what is offered currently it looks like there are only beta-versions of hardware with SATA-3 and USB 3 support available on the marked (according to tests there is a lot of variance of the max speed the controllers are able to achieve, bugs in the BIOS, or the controllers are attached to a slow bus which prevents to use the full bandwidth). So it will not be a new system soon.
As I had a 1GB USB-stick around, I decided to attach it to the one of the EHCI USB ports and use it as a cache device for ZFS. If someone wants to try this too, be careful with the USB ports. My mainboard has only 2 USB ports connected to an EHCI, the rest are UHCI ones. This means that only 2 USB ports are fast (sort of… 40 MBit/s), the rest is only usable for slow things like a mouse, keyboard or a serial line.
Be warned, this will not give you a lot of bandwidth (if you have a fast USB stick, the 40MBit/s of the EHCI are the limit which prevent a big streaming bandwidth), but the latency of the cache device is great when doing small random IO. When I do a gstat and have a look how long a read operation takes for each involved device, I see something between 3 msec and 20 msec for the harddisks (depending if they are reading something at the current head position, or if the harddisk needs to seek around a lot). For the cache device (the USB stick) I see something between around 1 mssec and 5 msec. That is 1/3th to 1/4th of the latency of the harddisks.
With a “zfs send” I see about 300 IOops per harddisk (3 disks in a RAIDZ). Obviously this is an optimum streaming case where the disks do not need to seek around a lot. You see this in the low latency, it is about 2 msec in this case. In the random-read case, like for example when you run a find, the disks can not keep this amount of IOops, as they need to seek around. And here the USB-stick shines. I’ve seen upto 1600 IOops on it during running a find (if the corresponding data is in the cache, off course). This was with something between 0.5 and 0.8 msec of latency.
This is the machine at home which is taking care about my mails (incoming and outgoing SMTP, IMAP and Webmail), has a squid proxy and acts as a file server. There are not many users (just me and my wife) and there is no regular usage pattern for all those services. Because of this I did not do any benchmark to see how much time I can gain with various workloads (and I am not interested in some artificial performance numbers of my webmail session, as the browsing experience is highly subjective in this case). For this system a 1 GB USB stick (which was just collecting dust before) seems to be a cheap way to improve the response time for often used small data. When I use the webmail interface now, my subjective impression is, that it is faster. I am talking about listing emails (subject, date, sender, size) and displaying the content of some emails. FYI, my maildir storage has 849 MB with 35000 files in 91 folders.
Bottom line is: do not expect a lot of bandwidth increase with this, but if you have a workload which generates random read requests and you want to decrease the read latency, it could be a cheap solution to add a (big) USB stick as a cache device.
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I experimented a little bit with the order of directories to backup in tarsnap.
Currently I use the following sorting algorithm:
- least frequently changed directory-trees first
Every change — even in meta-data — will affect the following data, as tarsnap is doing the de-duplication in fixed-width blocks (AFAIR 64k).
- for those directory-trees which change with the same frequency: list the bigger ones first
Implicitly I assume that the smaller ones are much smaller than the bigger ones so that the smaller part which will be backed up will not be noticed because of the bigger change. For my use cases of tarsnap this is true.
- if changes in a directory-tree are much much bigger than anything else, but the directory-tree has a medium change-frequency, put it even before less-frequently changing stuff
I do not want that a small change triggers a big backup, but a big backup can contain the remaining small part.
- if you backup home directories (even root’s one) and they do not contain much data, put them before directory-trees which change a lot daily
I do not want that a login triggers the transfer of data in other directory-trees which have not changed.
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I had a look at all my posts and determined which ones provide a mid-term / long-term benefit to readers. Those I classified for myself as Very Important Posts (for an appropriate definition of very and important…) and they are listed on the VIP page now.
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