My backup ZFS machine

 Posted by  Linux  No Responses »
Jun 262017
 

With my current ZFS pool getting close to its 2 TB limit I started to think about expanding it a bit. However, before doing anything with main NAS server, I decided to get the backup server up to speed. Reason is simple: while I am not a ZFS newbie, I don’t move pools on regular basis and moving backup server’s data will give me nice practice opportunity so I have procedure pinned down when I go to deal with the main storage.

My main parameters were to build machine capable of at least ZFS mirror, be reasonably easy to hide as it will be situated in living room, be as quiet as possible, and cost no more than $300 for all the hardware excluding disks. Note that nowhere I have any conditions on its speed – it is a backup machine I hopefully will never touch again.

For the case I went with Supermicro SC504-203B 19″ 1U rack mountable chassis. Some of you might be reasonable wondering which drugs I am taking that causes me to think of 19″ rack case as unobtrusive and easy to fit in living room. Well, you are missing a detail that my TV stand is piece of solid wood with opening that is about 25″ wide and 2″ tall. Just enough for me to slide the case below and for it never to be visible again.

As point of interest, you might notice Supermicro offers SC504-203B and SC505-203B rack cases that have seemingly identical specs. It took me a while to figure out the only difference: 504 has all the connectors in the back and 505 has the motherboard connectors at the front. For my case, more common setup of connectors at the back was better, but your mileage might vary.

Other than its perfect size, this case is one of rare in the lower price range to have enough place for two 3.5″ drives. As I am really not too happy with my current situation of backup on a single (albeit) ZFS-formatted drive, upgrading backup to a mirrored combo seemed like a long delayed improvement. Other than that, case has an efficient power supply (80+ Gold) alongside a wide selection of compatible boards.

And there is also a bummer – not all mini-ITX boards can fit this case. Better said, they will fit the case but their IO shield will be a tad too high for an 1U format. Yes, you can always go without the shield or by frankensteining the solution but I actually found a reasonably priced Supermicro board.

I decided to go with X10SBA-L board instead of similarly priced but seemingly more powerfull X10SBA. The “L” board doesn’t have additional Marvell chip and thus it has only two SATA 2.0 ports (Marvell brings additional four SATA 3.0 ports), it has one USB 3.0 and three USB 2.0 ports where Marvell offers additional two 2.0 ports, it has m-SATA port (which cannibalizes one of SATA 3.0 ports), and lastly it lacks eDP. For me neither of those were breaking deal as I intended to use only two disks with the single USB 3.0 port carrying Nas4Free installation.

A bit controversial decision is lack of ECC memory support that is not really frowned upon when dealing with ZFS. In reality, I couldn’t find any ECC board that would fit within my budget. And, while memory is important for ZFS, let’s not forget that this is just a backup machine and that memory errors are usually not catastrophic. Plan is to have ECC RAM on my next ZFS server. But my backup server – mah…

Speaking of memory, I essentially selected the cheapest 2x 4GB modules from manufacturer I trust. While I have bought Crucial, I would have taken Corsair, Kingston, or Samsung the same.

For disks I opted to go with WD Red 4TB model for now. As my current data actually fits into 2.5″ 2TB drive, space-wise I have quite a buffer for the next year and probably much longer. I was toying with the idea to use Seagate Ironwolf due to its attractive 6TB price, but noise level made me stick with WD Red. To minimize any potential issue affecting the whole batch, I actually bought disks at two different places (NewEgg and B&H).

A few curiosities were observed while pairing motherboard and case. First one is lack of opening for display port on the back. While slightly annoying, I found it bearable since HDMI opening, while grossly oversized, was accessible. If you really need display port you can order separate part number MCP-260-00068-0B but it will cost you $25.

Another one is mismatch between chassis power supply that has only 20-pin ATX connector and motherboard that requires 24-pin connector. As motherboard is really modest as far as power consumption goes, plugging 20-pin connector and leaving 4 leftmost pins empty works fine.

I also connected front-panel connector to PCI bracket in order to bring those ports to the outside. I only did it because I had bracket already available. Likewise, I swapped SATA cables that arrived with motherboard with shorter, round ones. This is just purely for cosmetics.

Without further ado, here is the itemized list:

Supermicro SuperChassis 504-203B $100
Supermicro X10SBA-L $149
Crucial 8GB DDR3L Kit (2 x 4GB) $54
WD Red 4TB (2x) 2x $137
USB 2.0 header to PCI bracket –
SATA cable, 6″, right-angle –
Total $577

Watching sector count

 Posted by  Uncategorized  No Responses »
Jun 212017
 

Ever since I first dealt with RAID, I was taught and was witness to ugly fact that two disks marked with the same size might not be exactly the same. Even the same disk from the same manufacturer could have slight difference in number of sectors. And some manufacturers were notorious for this (yes, Sun/Oracle, I am looking at you.

It was common wisdom to always make RAID a bit smaller than your full drive size to accommodate for potential “shrinkage” in the future. And I was myself known to warn others. However, things change…

Believe it or not, these days all disks have completely standardized sector count. For 512b sector size, formula is:

97,696,368 + (1,953,504 * CapacityInGB – 50))

For 4K sectors, formula is:

12,212,046 + (244,188 * CapacityInGB – 50))

This is courtesy of LBA Count for Disk Drives Standard (LBA1-03) that is seemingly followed by all manufacturers. I couldn’t find a single drive not following this standard and I’ve tried.

What does this mean? It means, if you have drive that is manufacturer in last five years, you can forget about under-sizing your RAID. Any replacement drive you order will have exactly the same sector count as long as sector size is same.

PS: Find below table for disks with 4K sectors:

Size LBA sector count
1 TB 244,190,646
2 TB 488,378,646
3 TB 732,566,646
4 TB 976,754,646
6 TB 1,465,130,646
8 TB 1,953,506,646
10 TB 2,441,882,646

PPS: While these rules are valid for SSDs too, depending on their configuration (e.g. over-provisioning) exact sector count available to end-user might vary.

WRT Settings 1.20

 Posted by  Updates  No Responses »
Jun 162017
 

Since I created WRT settings there weren’t too many versions. It is as simple as it gets – you have list of name value pairs, formats are well defined and that’s it.

However, Iv7777 found an issue in way how encryption works for AsusWRT v2 configuration format. He has a bit longer explanation in addition to his fix. Short version is that some random values are not working properly with Asus’ configuration file encryption. Leaving aside discussion on how useful this encryption is in the first place, I give you new version with this correction.

In addition to this major issue, there is a bugfix for handling empty DD-WRT files and program has been upgraded to use .NET Framework 4.

As always, new version is available either from application itself or from project’s page.

Weirdest feature in C# 7

 Posted by  Programming  No Responses »
Jun 112017
 

I love the new C# 7 candy. Some of them I use, some of them I will use rarely. However, there is one I don’t get at all.

Let’s imagine having a login class and a single method with kinda unusual out parameters:

public class Login {
    public string UserName { get; set; }
    public string Password { get; set; }

    public void Deconstruct(out string userName, out string password) {
        userName = UserName;
        password = Password;
    }
}

Normally you would expect to call this method as:

var login = new Login(...);

var userName, var password;
login.Deconstruct(out userName, out password);

With new out variables, this can be written a bit shorter and, in my opinion, more readable:

var login = new Login(...);
login.Deconstruct(out var userName, out var password);

What I wouldn’t expect for the life of me, would be a Tuple-like syntax:

(var userName, var password) = login;

Why?

Because it doesn’t use keyword, it doesn’t use interface, it doesn’t use attribute. Nope, it uses the magic method name. Yep method must be named Deconstruct and have two or more output parameters and the new syntax is yours to abuse.

And this is not me not liking tuples. I would be more than happy if this worked as a normal tuple returned from a more standard method call , e.g.:

(var userName, var password) = login.Deconstruct();

    public (string userName, string password) Deconstruct() {
        return (UserName, Password);
    }

I believe this magic name method is just simply a wrong way to introduce the new features. It is not discoverable, it doesn’t really read well, and it paves path for introduction of other magical method names. Didn’t IDispose and its Dispose() vs Dispose(bool) teach us anything?

I can just hope this single deviant feature among other sensible C# 7 features is just a price we pay for the night Hejlsberg got drunk. And I surely hope he will stay clean for C# 8. :)

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