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1clue
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PostPosted: Tue Jul 16, 2013 3:13 am    Post subject: Raid in a hurry on WD green? -- solved Reply with quote

Hi,

I'm in a hurry for a bit of storage. I was hoping for raid 1. I'm in a small town, picked up a couple external drives because they don't carry internals here. I peeked under the covers and found out they're 3t western digital green drives. WD30EZRX, 64m cache.

So I'm using an Asus P6T motherboard, it's just software RAID.

I've done raid before several times, just curious if it's a good idea to do it on a green drive. I'd hate to waste an extra day or two, but if necessary I can return these and order something.


Last edited by 1clue on Fri Jul 19, 2013 10:54 pm; edited 1 time in total
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frostschutz
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PostPosted: Tue Jul 16, 2013 9:26 am    Post subject: Reply with quote

I have a NAS with 4x2TB (mdadm RAID5), my desktop used to have 2x2TB (mdadm RAID 1) but I added a 3TB disk so it's RAID 5 now (excluding the surplus 1TB which is used for Windows).

All WD Green drives. I'm very happy with them, oldest one has >12000 power on hours and still fine. However none of my boxes run 24/7.
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1clue
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PostPosted: Tue Jul 16, 2013 3:41 pm    Post subject: Reply with quote

OK good.

My first raid setup was WD green, it died early. I've since learned about a fix for LOAD_CYCLE_COUNTS on some drives, I wonder if that's what my first setup had a problem with.

I think I'll use these, I at least will be going in with open ey.es this time.

Thanks.
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Ant P.
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PostPosted: Wed Jul 17, 2013 8:26 pm    Post subject: Reply with quote

If you use WD green in a RAID you'll probably want to adjust the idle3 value to something more appropriate before using them - check the -J flag in `man hdparm`.
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PostPosted: Wed Jul 17, 2013 9:26 pm    Post subject: Reply with quote

1clue,

I have 5 2Tb WD Greens in my media server in raid5. Two of them died at 9 months old.
You will want to adjust the idle3 value - if you can WD has blocked it on some greens.

I won't be getting any more WD greens. Head unloading after 8 seconds of no use is just silly.
Removing the idle3 timeout tweak so you can fix it is just stupid.
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1clue
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PostPosted: Thu Jul 18, 2013 12:32 am    Post subject: Reply with quote

Neddy,

Sorta too late for that now, but thanks. I've already got them in and formatted as Linux raid autodetect.

Got another problem though, they're 3T drives set up as raid 1. But I get this:


root@chronos:~# vgs
VG #PV #LV #SN Attr VSize VFree
hddvg1 1 5 0 wz--n- 698.63g 435.15g
rd1vg1 1 0 0 wz--n- 746.39g 746.39g
ssdvg1 1 1 0 wz--n- 223.07g 204.44g
root@chronos:~# fdisk -l /dev/sdb

Disk /dev/sdb: 3000.6 GB, 3000592982016 bytes
90 heads, 3 sectors/track, 21705678 cylinders, total 5860533168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x345a0cea

Device Boot Start End Blocks Id System
/dev/sdb1 3 1565565871 782782934+ fd Linux raid autodetect
Partition 1 does not start on physical sector boundary.


Basically I have 1.5T in my md0, it should be 3T, and it appears that my VG has only 750G.

Is there a limit I don't know about?
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PostPosted: Thu Jul 18, 2013 5:22 pm    Post subject: Reply with quote

1clue,

You must not use a MSDOS Partition table. At most it can describe 2TiB of space.
Thats 2^32 sectors of 512B. You drives are bigger than that so the rest of the drive has vanished.

You need to use GPT and make sure that your partitions all start on a 4096B boundary or writes will be very slow.

You will need to add GPT support to your kernel.

Make friends with parted and choose GPT disk labels.
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frostschutz
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PostPosted: Thu Jul 18, 2013 7:18 pm    Post subject: Reply with quote

Ant P. wrote:
check the -J flag in `man hdparm`.


Oh, hdparm has a flag? I use sys-apps/idle3-tools

Forgot to mention, I turn it off on all my disks, no ill effects so far.
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1clue
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PostPosted: Thu Jul 18, 2013 10:31 pm    Post subject: Reply with quote

@NeddySeagoon, You just ruined my day. Parted wasn't around when I got into Linux, and I haven't gotten around to learning the newfangled stuff yet. :)

@Frostschutz, I'll try it, but haven't gotten around to that yet. I still gotta reformat and maybe compile the kernel.

Just out of curiosity, I wonder what would happen if I made 2 partitions per drive, made them Linux raid autodetect, and then added them to the array? Would the RAID and LVM tools be smart enough to figure that out?

Not sure I want to mess with it now anyway but if one of you knows I'd love to hear about it.

Thanks guys.
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PostPosted: Thu Jul 18, 2013 10:59 pm    Post subject: Reply with quote

sys-apps/gptfdisk if you do not like parted.
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1clue
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PostPosted: Thu Jul 18, 2013 11:05 pm    Post subject: Reply with quote

I'm just being grouchy. Fdisk has worked to date, now it's obsolete and I actually ran into a problem because of it.

It's like if your favorite dog died. I'll miss him.
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PostPosted: Fri Jul 19, 2013 5:44 pm    Post subject: Reply with quote

1clue,

fdisk has run out of bits in partition table entries. Its been obsolete for a long time.
Its as broken as CHS addressing on your 3T HDD. Mourn and move on.

The whole partition table in the free space at the end of the MSDOS boot loader was a dirty hack to cope with HDD bigger than 32Mb (yes MB)
The extended partition was another dirty hack to cope with HDD > 128Mb. (still Mb)
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1clue
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PostPosted: Fri Jul 19, 2013 8:12 pm    Post subject: Reply with quote

I remember using 20m hard disks when they were new and stylish. Compared to a 5.25" floppy they were huge. And noisy and heavy. I was in high school, and that should pretty much place me for anyone who was curious.
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PostPosted: Wed Jul 24, 2013 2:54 am    Post subject: Reply with quote

I've seen a bunch of older 20M disks, most of them, even with their stepper motors, aren't way too bad I'd have to say.

Though I still need to go find the notable exception - a miniscribe 8425 - you wouldn't believe how noisy this thing was. A half height 5.25" internal HDD that took 90-100ms to seek making this quite characteristic screech, along with the spindle motor that could wake up the dead...

Nevertheless, running it at 1:1 interleave it was as fast as any other disk in its day...
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PostPosted: Wed Jul 24, 2013 12:24 pm    Post subject: Reply with quote

NeddySeagoon wrote:
1clue,

You must not use a MSDOS Partition table. At most it can describe 2TiB of space.
Thats 2^32 sectors of 512B. You drives are bigger than that so the rest of the drive has vanished.

You need to use GPT and make sure that your partitions all start on a 4096B boundary or writes will be very slow.

You will need to add GPT support to your kernel.

Make friends with parted and choose GPT disk labels.


With reference to this thread ( https://forums.gentoo.org/viewtopic-t-963286-highlight-.html ) I'll have to admit to being in the "crusty" camp. My first Linux install was RedHat 4.0 (Not RedHat Enterprise, either) when it was brand new. For that install I used good old "fdisk", and have been using it ever since. I have a bootable disk with "gparted" and have used that from time to time, but my installs have generally been from a Gentoo minimal disk or SystemRescueCD. I'll admit that I've never used "parted" from the command line. (Looking at the man page now...) I've also never used a GPT disk.

So it looks like it's time for me to change a bit, time to update.

1 - It looks to me as if parted is more complete than fdisk - that I can partition the disk and make filesystems both. True? (I now see that they recommend using separate mkfs - no big deal.)
2 - A year or two back I helped a friend set up 2TB drives in a machine at work, and we had to do non-standard alignment stuff under fdisk. It looks like parted may handle this more easily. I see that I probably want "-a optimal" at startup, and I'm all set. True?
3 - Will this work with good old grub, or do I have to move to grub2 or some other bootloader?
4 - Can an MSDOS disk be converted to GPT? My next installation will probably be as a dual-boot on an existing Windows machine. I'm wondering if I can experiment with this there, or if it will have to wait for a fresh install.

Thanks...
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1clue
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PostPosted: Wed Jul 24, 2013 2:50 pm    Post subject: Reply with quote

I found something called gdisk that is more fdisk-like and handles gpt partitions. Seems to be missing alignment checks though.
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PostPosted: Wed Jul 24, 2013 4:53 pm    Post subject: Reply with quote

I think most recent partitioning software partitions on MegaByte (actually, Mebibyte, make sure it's 1024 byte not 1000) boundaries instead of C/H/S. By default, if you put your partitions on MB boundaries it should be aligned just fine for most disks (4K "advanced" and SSD).

However if you have an ancient HDD where C/H/S is mapped straight to the interface, then having partitions straddle cylinder boundaries could make some weird performance issues as it would have to do a seek during a seemingly contiguous read.

Then again it probably would have seeked anyway during that file transfer...
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