RE: RAID1 synchronisation - howto OR not necessary?
-Original Message- From: Jan Catrysse Sent: Thursday, November 22, 2007 2:18 PM To: 'freebsd-questions@freebsd.org' Subject: RAID1 synchronisation - howto OR not necessary? Dear subscribers, I am currently running a production server: FreeBSD 6.2 STABLE Onboard Intel ICH8R Raid 1 with 2x SATA300 500GB HDD Using ATA for Raid1 On Windows systems it is an absolute must to do a Raid Synchronisation every once and a while to maintain data consistency. I am some what disturbed that that kind of command / tool seems not available on FreeBSD. Are there other methods to do the synchronisation? 1) Maybe atacontrol detach atacontrol addspare atacontrol rebuild? 2) Maybe data consistency is always maintained automatically by the driver? 3) Maybe I have to panic and urgently make backups? Kind regards, Jan Catrysse I have gotten some feedback from the ATA(4) developer and pasted it beneath. Regards Jan Catrysse Synchronisation should not be needed at all, however if you want to do it #1 above is the way. ATA will always return error to the upper layers if one of the writes to either drive fails, and will then mark the array as degraded, so there should be no need to do and sync unless you change one of the drives. If you zero out both drives before creating the RAID1 you can do a simple cmp adX adY of the two disks in the mirror to verify they are equal, except for the RAID metadata normally located at the last 63 sectors of the media (depends on meta data format). Note that you *HAVE* to zero out the disks first before use in that case, as ATA has no idea which blocks are used and which are not, and in the case of unused areas you will get differences if the disks wasn't cleared before use. ATA only makes certain that data *written* hits both disks and in case not returns error to the upper layers and marks the array as degraded. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
RE: RAID1 synchronisation - howto OR not necessary?
From: Bill Moran [mailto:[EMAIL PROTECTED] Sent: Thursday, November 22, 2007 9:57 PM To: Jan Catrysse Cc: freebsd-questions@freebsd.org Subject: Re: RAID1 synchronisation - howto OR not necessary? Jan Catrysse [EMAIL PROTECTED] wrote: Dear subscribers, I am currently running a production server: FreeBSD 6.2 STABLE Onboard Intel ICH8R Raid 1 with 2x SATA300 500GB HDD Using ATA for Raid1 On Windows systems it is an absolute must to do a Raid Synchronisation every once and a while to maintain data consistency. Wow. Any RAID controller with that requirement is junk. Where did you get the information from that you had to synchronize? Does it say so in the manual? Does it actually say every once and a while or does it give a specific schedule. I suspect that you have wrong information ... but if your information is correct, I'd get a refund on that RAID controller. I am some what disturbed that that kind of command / tool seems not available on FreeBSD. There is not, because such a thing should not be necessary. Are there other methods to do the synchronisation? 1) Maybe atacontrol detach atacontrol addspare atacontrol rebuild? 2) Maybe data consistency is always maintained automatically by the driver? 3) Maybe I have to panic and urgently make backups? If resyncing your raid on a regular basis is truly a requirement, I'd do #3 at least, followed by getting my money back. Hi Bill, Thank you for your input. I assumed this was common knowledge, but I can be wrong? I've checked some other RAID controllers in the company and all of them have the need to be verified/synchronized once and a while. This happens in the BIOS for the more expensive cards ( 600€) and with a utility/driver for the low budget cards... In my case I am using a real inexpensive onboard Intel ICH8R controller but I presume even a low cost controller needs to do the job done. Furthermore it's only a simple mirror... Intel provides a small windows utility to synchronize. This is what I found in a 3Ware manual: Verification can provide early warning of a disk drive problem or failure. ...verification once every 24 hours... Not verifying the unit periodically can lead to an unstable array unit and may cause data loss. It is strongly recommended that you schedule a verify at least 1 time per week. For a RAID 1 or RAID 10 unit, a verify compares the data of one mirror with the other. For RAID 5, RAID 6, and RAID 50, a verify calculates parity and compares it to what is written on the disk drive. Cheers, Jan ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: RAID1 synchronisation - howto OR not necessary?
Jan Catrysse [EMAIL PROTECTED] wrote: I didn't dig in GEOM because I wondered what happens if the primary disk fails when two disks are in a RAID1 config? There is no primary disk in a GEOM RAID1. If the BIOS has a concept of primary disk, then it's a BIOS issue and the answer will depend on the BIOS. -- Bill Moran http://www.potentialtech.com ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
RE: RAID1 synchronisation - howto OR not necessary?
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bill Moran Sent: Friday, November 23, 2007 3:28 PM To: Jan Catrysse Cc: freebsd-questions@freebsd.org Subject: Re: RAID1 synchronisation - howto OR not necessary? Jan Catrysse [EMAIL PROTECTED] wrote: Hi Bill, Thank you for your input. I assumed this was common knowledge, but I can be wrong? I've checked some other RAID controllers in the company and all of them have the need to be verified/synchronized once and a while. No. There is a _world_ of difference between verify and synchronize. Periodically verifying the health of a RAID array is good practice. Re-synchronizing it periodically is stupid. If you have to do that, then you wasted money on a RAID card. This happens in the BIOS for the more expensive cards ( 600€) and with a utility/driver for the low budget cards... Depends on what you're talking about. Yes, expensive cards do both health checking and resyncing in the BIOS without the need of operator intervention. Low-end hot-swappable cards will automatically do the resynchronizing if they detect a HDD change, but often don't do periodic health checking. Low-end cards do neither. However, you have to power the machine down to replace a failed drive, so you're also accepting the burden of waiting for the BIOS to resync. It's part of the cost trade-off. This is what I found in a 3Ware manual: Verification can provide early warning of a disk drive problem or failure. ...verification once every 24 hours... Not verifying the unit periodically can lead to an unstable array unit and may cause data loss. It is strongly recommended that you schedule a verify at least 1 time per week. Nice documentation ... Do you verify every 24 hours or once a week? In any event, the availability of such a utility for FreeBSD depends on the driver and the (possible) availability of third-party (or even vendor-supplied) utilities. For example, LSI provides the megaraid utility. It's designed for Linux but works on FreeBSD and allows total control over the RAID card, including verifications. Reading the man page for the driver being used may turn up something. I don't know if one exists for your specific card, but keep in mind that the driver you're using may also work with high-end RAID systems that don't need it, so the absence of one is possible. I suggest you reformat/repost your question with a subject line more along the lines of Looking for a control utility for ICH8R RAID It's quite possible that the people who know a lot about that hardware missed the original conversation thread. If there is no such utility, I suggest looking into something like samhain, which will continually validate that the files on your system are uncorrupted. This has the added advantage of warning you if someone has cracked your system and installed a trojan. Also consider the benefit of spending the extra $$ on a high-end RAID card. There are very good reasons that people are willing to pay more for them. Personally, I wouldn't use a low-end RAID card ... GEOM would be just as good if not better, IMHO. Hello again, I understand what you mean by synchronization not beeing the same as data verification. What I mean is indeed data verification. For the Intel ICH8R controller FreeBSD uses ATA(4), no vendor support is available. It is possible however to control the array using ATACONTROL STATUS / DETACH / ADDSPARE / REBUILD / ... but no VERY command seem to exist. As you suggest I will repost the question with another subject. Would it be a big problem if I contact the FreeBSD developper of ATA(4) directly? I didn't dig in GEOM because I wondered what happens if the primary disk fails when two disks are in a RAID1 config? Cheers, Jan ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
RE: RAID1 synchronisation - howto OR not necessary?
-Original Message- From: Bill Moran [mailto:[EMAIL PROTECTED] Sent: Friday, November 23, 2007 4:01 PM To: Jan Catrysse Cc: freebsd-questions@freebsd.org Subject: Re: RAID1 synchronisation - howto OR not necessary? Jan Catrysse [EMAIL PROTECTED] wrote: I didn't dig in GEOM because I wondered what happens if the primary disk fails when two disks are in a RAID1 config? There is no primary disk in a GEOM RAID1. If the BIOS has a concept of primary disk, then it's a BIOS issue and the answer will depend on the BIOS. I will take a look at GEOM. Hopefully I have some feedback on my new post, to be sure I've changed synchronization by verification this time :-) Regs, Jan ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: RAID1 synchronisation - howto OR not necessary?
Jan Catrysse [EMAIL PROTECTED] wrote: From: Bill Moran [mailto:[EMAIL PROTECTED] Jan Catrysse [EMAIL PROTECTED] wrote: Dear subscribers, I am currently running a production server: FreeBSD 6.2 STABLE Onboard Intel ICH8R Raid 1 with 2x SATA300 500GB HDD Using ATA for Raid1 On Windows systems it is an absolute must to do a Raid Synchronisation every once and a while to maintain data consistency. Wow. Any RAID controller with that requirement is junk. Where did you get the information from that you had to synchronize? Does it say so in the manual? Does it actually say every once and a while or does it give a specific schedule. I suspect that you have wrong information ... but if your information is correct, I'd get a refund on that RAID controller. I am some what disturbed that that kind of command / tool seems not available on FreeBSD. There is not, because such a thing should not be necessary. Are there other methods to do the synchronisation? 1) Maybe atacontrol detach atacontrol addspare atacontrol rebuild? 2) Maybe data consistency is always maintained automatically by the driver? 3) Maybe I have to panic and urgently make backups? If resyncing your raid on a regular basis is truly a requirement, I'd do #3 at least, followed by getting my money back. Hi Bill, Thank you for your input. I assumed this was common knowledge, but I can be wrong? I've checked some other RAID controllers in the company and all of them have the need to be verified/synchronized once and a while. No. There is a _world_ of difference between verify and synchronize. Periodically verifying the health of a RAID array is good practice. Re-synchronizing it periodically is stupid. If you have to do that, then you wasted money on a RAID card. This happens in the BIOS for the more expensive cards ( 600€) and with a utility/driver for the low budget cards... Depends on what you're talking about. Yes, expensive cards do both health checking and resyncing in the BIOS without the need of operator intervention. Low-end hot-swappable cards will automatically do the resynchronizing if they detect a HDD change, but often don't do periodic health checking. Low-end cards do neither. However, you have to power the machine down to replace a failed drive, so you're also accepting the burden of waiting for the BIOS to resync. It's part of the cost trade-off. This is what I found in a 3Ware manual: Verification can provide early warning of a disk drive problem or failure. ...verification once every 24 hours... Not verifying the unit periodically can lead to an unstable array unit and may cause data loss. It is strongly recommended that you schedule a verify at least 1 time per week. Nice documentation ... Do you verify every 24 hours or once a week? In any event, the availability of such a utility for FreeBSD depends on the driver and the (possible) availability of third-party (or even vendor-supplied) utilities. For example, LSI provides the megaraid utility. It's designed for Linux but works on FreeBSD and allows total control over the RAID card, including verifications. Reading the man page for the driver being used may turn up something. I don't know if one exists for your specific card, but keep in mind that the driver you're using may also work with high-end RAID systems that don't need it, so the absence of one is possible. I suggest you reformat/repost your question with a subject line more along the lines of Looking for a control utility for ICH8R RAID It's quite possible that the people who know a lot about that hardware missed the original conversation thread. If there is no such utility, I suggest looking into something like samhain, which will continually validate that the files on your system are uncorrupted. This has the added advantage of warning you if someone has cracked your system and installed a trojan. Also consider the benefit of spending the extra $$ on a high-end RAID card. There are very good reasons that people are willing to pay more for them. Personally, I wouldn't use a low-end RAID card ... GEOM would be just as good if not better, IMHO. -- Bill Moran http://www.potentialtech.com ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: RAID1 synchronisation - howto OR not necessary?
Hi, On 23/11/2007, Jan Catrysse [EMAIL PROTECTED] wrote: From: Bill Moran [mailto:[EMAIL PROTECTED] Sent: Thursday, November 22, 2007 9:57 PM To: Jan Catrysse Cc: freebsd-questions@freebsd.org Subject: Re: RAID1 synchronisation - howto OR not necessary? Jan Catrysse [EMAIL PROTECTED] wrote: [...] This is what I found in a 3Ware manual: Verification can provide early warning of a disk drive problem or failure. [...] Yes, it deals with drives failing silently. It's possible that data on a disk can get corrupted. You don't see the error until you read the block the next time. AFAIK the data contained in the bad block is delivered to the CPU/RAM and can cause some damage there. The problem I see with this setup is that you can't know which block is the one that is okay. You need some additional feature like a checksum for each block to check which one is correct. This isn't supported by all file systems, so you can only see that there is a difference between two blocks which sould normally be identical. I doubt that cheep RAID-Controllers have this capability, so you have to stick to some software solution. Does FreeBSD take care about something like this, I mean for software RAIDs? Regards Christian ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: RAID1 synchronisation - howto OR not necessary?
On Fri, Nov 23, 2007 at 02:45:37PM +0100, Christian Walther wrote: Hi, On 23/11/2007, Jan Catrysse [EMAIL PROTECTED] wrote: From: Bill Moran [mailto:[EMAIL PROTECTED] Sent: Thursday, November 22, 2007 9:57 PM To: Jan Catrysse Cc: freebsd-questions@freebsd.org Subject: Re: RAID1 synchronisation - howto OR not necessary? Jan Catrysse [EMAIL PROTECTED] wrote: [...] This is what I found in a 3Ware manual: Verification can provide early warning of a disk drive problem or failure. [...] Yes, it deals with drives failing silently. It's possible that data on a disk can get corrupted. You don't see the error until you read the block the next time. AFAIK the data contained in the bad block is delivered to the CPU/RAM and can cause some damage there. The problem I see with this setup is that you can't know which block is the one that is okay. You need some additional feature like a checksum for each block to check which one is correct. This isn't supported by all file systems, so you can only see that there is a difference between two blocks which sould normally be identical. The disks themselves handle the checksumming to detect bad blocks. With modern disks it is *very* rare that a block on the disk goes bad without the disk being able to report it it as such. This means that if you have a functioning RAID1 setup and one of the disks report a bad block, then the controller can simply read the corresponding block from the other disk, and rewrite it to the disk with the bad block. If a disk has problems writing a block it will transparently re-map the block to another. The problems can occur when one disk in a RAID-array has failed and you try to rebuild it from the other disk(s). If you then encounter a bad block on that disk you have a problem since you don't have a good copy of that block. This is what verification (which, btw, is not the same as synchronization) tries to prevent by reading every block on each disk on a regular basis. Then the RAID controller can recover the data on any bad blocks from the other disk(s) in the array. I doubt that cheep RAID-Controllers have this capability, so you have to stick to some software solution. Does FreeBSD take care about something like this, I mean for software RAIDs? The cheap RAID-controller do almost all the RAID-operations in software anyway so it does indeed have to be a software solution anyway. I don't think FreeBSD's software RAID implementations have any support for disk verification - at least I couldn't find anything when doing a quick read through the man-pages. -- Insert your favourite quote here. Erik Trulsson [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: RAID1 synchronisation - howto OR not necessary?
Jan Catrysse [EMAIL PROTECTED] wrote: Dear subscribers, I am currently running a production server: FreeBSD 6.2 STABLE Onboard Intel ICH8R Raid 1 with 2x SATA300 500GB HDD Using ATA for Raid1 On Windows systems it is an absolute must to do a Raid Synchronisation every once and a while to maintain data consistency. Wow. Any RAID controller with that requirement is junk. Where did you get the information from that you had to synchronize? Does it say so in the manual? Does it actually say every once and a while or does it give a specific schedule. I suspect that you have wrong information ... but if your information is correct, I'd get a refund on that RAID controller. I am some what disturbed that that kind of command / tool seems not available on FreeBSD. There is not, because such a thing should not be necessary. Are there other methods to do the synchronisation? 1) Maybe atacontrol detach atacontrol addspare atacontrol rebuild? 2) Maybe data consistency is always maintained automatically by the driver? 3) Maybe I have to panic and urgently make backups? If resyncing your raid on a regular basis is truly a requirement, I'd do #3 at least, followed by getting my money back. -- Bill Moran http://www.potentialtech.com ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
